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MINERALIDENTIFICATION TABLE 1 – MINERAL LUSTER

Luster – The most useful subdivision of luster is whether a mineral has metallic or
nonmetallic luster.

Metallic Luster Streak color can help in identification, especially for
hematite. Some observers see more subtle variations in streak color.

Mineral Name Specific Luster Streak Color

Chalcopyrite brass or gold dark gray

Native Copper coppery copper

Galena silvery dark gray

Graphite silvery dark gray

Hematite steel, but see below brick red

Magnetite broken cast iron dark gray

Pyrite brass dark gray

Sphalerite steel, but see below pale yellow

Nonmetallic – All other minerals in the lab set including hematite and
sphalerite have nonmetallic lusters. A more detailed analysis of nonmetallic
luster can help. Some minerals may exhibit more than one type of nonmetallic
luster depending on crystal habit. Following are some examples of specific
lusters. Different observers often have different opinions on luster
appearance. Semantics aside, experience is the best way to develop expertise.

Specific Luster Example Minerals

Glassy or Vitreous olivine, quartz

Waxy cryptocrystalline quartz, talc

Pearly muscovite, biotite

Earthy or Dull nonmetallic hematite, limonite

Greasy calcium-rich plagioclase feldspar

Resinous nonmetallic sphalerite

Porcelaneous hornblende, potassium feldspar

MINERAL IDENTIFICATION TABLE 2 – HARDNESS

The following table lists mineral hardness using the Mohs scale. TEE Table 4.2,
page 88 lists the index minerals on this scale. Topaz and Diamond are not

included in the mineral identification exercise, but all other minerals in Table 4.2
are. The scale is not linear. In practice, the scratch tests are performed with

commonly available objects. These also are listed in Table 4.2, but not

accurately. Remember that harder materials with higher Mohs number scratch
softer materials with lower Mohs number. Substances of equal hardness scratch

each other with great difficulty.

Other common objects that can be used for hardness testing include copper
penny (Mohs 3.5), wire nail (Mohs 4.5), concrete nail (Mohs 5.5) steel file (Mohs
6.5), streak plate (Mohs 6.5), and quartz (Mohs 7). Nails and streak plates are

provided in the laboratory. Noting the ease or difficulty of scratching a material
will provide a useful clue about the precise hardness of a mineral. Some

pressure is needed to scratch glass with potassium feldspar, but quartz and
harder materials scratch the glass easily.

Minerals harder than a knife blade or glass plate; Mohs > 5.5

Mineral Mohs
Hardness

Comment

Corundum 9 Index mineral on Mohs scale

Garnet 7

Olivine 7

Quartz 7 Index mineral on Mohs scale

Cryptocrystalline Quartz 7 Be sure to test fresh mineral

Pyrite 6-6.5

Magnetite 6

Plagioclase Feldspar 6

Potassium Feldspar 6 Index mineral on Mohs scale

Hematite, metallic 6.5

Augite 5.5-6

Hornblende 5.5 Very difficult to scratch glass

Minerals softer than a glass plate but harder than a fingernail; Mohs 2.5-5.5

Mineral Mohs
Hardness
Comment

Hornblende 5.5 Very difficult to scratch glass

Hematite, nonmetallic 5

Goethite 5-5.5

Limonite 1.5-5.5 Varies because of structure

Apatite 5 Index mineral on Mohs scale

Fluorite 4 Index mineral on Mohs scale

Chalcopyrite 3.5-4

Azurite 3.5-4

Sphalerite 2.5-4

Dolomite 3.5-4

Barite 3-3.5

Calcite 3 Index mineral on Mohs scale

Biotite 2.5-3

Copper 2.5-3

Galena 2.5

Halite 2.5 Crumbles – false low hardness

Muscovite 2-2.5

Minerals softer than a fingernail; Mohs < 2.5

Muscovite 2-2.5 Difficult to scratch

Chlorite 2-2.5 Difficult to scratch

Gypsum 2 Index mineral on Mohs scale

Limonite 1.5-5.5 Fine grained crumbly form is soft

Graphite 1 Messy to handle

Talc 1 Index mineral on Mohs scale

MINERAL IDENTIFICATION TABLE 3 – CLEAVAGE

Minerals can be classified into two broad groups by whether or not cleavage is
obvious. This works well with large mineral grains with obvious broken

surfaces. Determining if cleavage is present can be difficult in fine-grained
specimens, though use of magnification can help. When uncertain as to the

presence of cleavage, ignore that property and try to identify the mineral with
other diagnostic properties.

If cleavage is observed, then determining the number of directions of cleavages
and the angle between cleavages will help to define the mineral. For example,

fluorite is the only mineral we study with 4 directions of cleavage.

TEE does not use the term direction of cleavage. Cleavage planes in a direction
of cleavage will all be parallel to each other. Any other directions of cleavage in
the mineral grain will have different orientations. When rotating a single mineral
grain under a light, the parallel planes of a direction of cleavage will all flash at

the same orientation of the mineral grain.

Cleavage can be classified further as to its quality and ease of forming. This
ranges from fair through good to perfect. In the latter case, cleavages will be

smooth and easily formed. This is less so with good cleavage, and poor cleavage
is difficult to form.

Two other types of surfaces occur on mineral grains. Fractures are irregular

surfaces from breakage on other than cleavage planes. The nature of the fracture
may be useful in determining the mineral name. When minerals grow

unrestricted, they develop crystals with well defined crystal faces. A crystal form
is all crystal faces related by symmetry. Some information about crystal forms

will be acquired in the basic study of minerals, and can be very useful for
identification. The study of crystal symmetry is beyond the scope of GO110,

though it is a fascinating subject.

Minerals that do not exhibit cleavage

Mineral Name Comments

Apatite Conchoidal fracture

Chalcopyrite Poor cleavage rarely seen

Copper Hackly fracture tends to grab skin when rubbed

Corundum

Garnet Widely spaced parting sometimes confused with cleavage

Goethite/Limonite

Hematite Brick red streak is diagnostic!

Magnetite Magnetic property is diagnostic!

Olivine Conchoidal fracture

Pyrite

Quartz Conchoidal fracture

Quartz, cryptoxln Conchoidal fracture

Talc has one direction of cleavage, but it often is to fine-grained to
show cleavage

Minerals that do exhibit obvious cleavage

Mineral
Name

Cleavage Directions Comments

Augite 2 at nearly 900

Barite 2 good; 1 excellent Cleavage results in platy appearance

Biotite 1 excellent Easy to cleave

Calcite 3 excellent not at 900 Rhombohedral cleavage

Chlorite 1 excellent Difficult to see when fine grained

Dolomite 3 excellent not at 900 Similar to calcite, usually small grains

Feldspars 2 good at 900

Fluorite 4 excellent Octahedral cleavage; diagnostic!

Galena 3 excellent at 900 Cubic cleavage

Graphite 1 excellent Excellent lubricant

Gypsum 2 poor; 1 excellent Difficult to see when fine grained

Halite 3 excellent at 900 Cubic cleavage

Hornblende 2 good at 600 and 1200

Muscovite 1 excellent Easy to cleave

Sphalerite 6 excellent Diagnostic, but finding all 6 is difficult

Geology is science that studies all physical aspects of the planet Earth and other planets. It is the

study of the history of the planet, the composition, the internal structure and the surface features of

that planet. We study our planet by field work, sample collecting and mapping. The samples can be

analyzed via chemical means as well as by optical means. Fossils are identified and correlated to age

and paleo-environments. Other related Earth sciences that are closely related to geology are

meteorology, oceanography and ecology. Subfields of geology are geochemistry, geophysics and

geo-biology. Other planets we study via remote sensing and by studying analysis sent by rovers of

samples that they have collected.

While geology is lumped as earth science and taught in high school to those who can’t handle

science like biology, chemistry or physics. In reality geology is a hybrid science requiring calculus,

chemistry through at least p-chem., and physics. On top of this knowledge add to it an

understanding of earth processes, mineralogy, and optics. Paleontology also requires knowledge of

biology as well.

Geologists are taxed with finding oil and coal for energy to power our modern economy. But this

is not only task that the geologist serves. Every bit of metal you use, every mine that is dug depends

of geologist. Modern batteries that may give us energy independence, materials used to build

photovoltaic cells and wind turbines are courtesy of geologist.

How does a geologist study the earth? Are we out there with rock hammers in hand and a pack

mule behind us? We use the same method as all other scientist- the scientific method. This method

calls for a hypothesis (possible explanation) for an event or series of events that have been

observed. A coherent set of hypothesis back by a large by of data both observational and by

laboratory measurements gives theory to explain a series of events. These theories obey the

physical laws or principles of how the universe works. Please notice that one part of the scientific

method is missing- experimentation in a controlled environment. It is impossible to do this when the

events we are theorizing about are global in nature and take place of millions to billions of years. To

deal with that we turn to the scientific model and create mathematical models that we try to

simulate what the Earth will do during time.

We use knowledge the data that formed the hypothesis and theories into a mathematical model

run through a computer to test the validity of our theories. But remember it is the same technique

that forecast the local weather. To improve the theory and model we continue to gather data. This

data is not only based on observations in the field (our geologist with the mule) but by using remote

sensing using satellite data, chemical and optical analysis of rocks.

From observation can the principle of uniformitarianism that can be paraphrased by the

statement that the present is the key to the past. The forces acting on our planet today are the same

forces that have acted on it in the past. This covers the slow steady process such as river moving

sediment to the ocean and the wind eroding a rock into strange shapes. It also allows for the

cataclysmic event like the earthquake, volcanic eruption and meteor impact. Most geologic process

takes thousands to millions of years, though.

The first part of understanding geology is understanding the makeup of the planet itself. The

size of the planet was determined 250 BC by a Greek performing an experiment. His estimate of

40,000 km with a radius of 6370 km and was surprisingly accurate. A more precise measurement

was achieved in the 1800’s found that the earth is not a perfect sphere. It bulges out slightly at the

equator and is smashed slightly at the poles.

The Earth is not a smooth sphere as it appears in

space. Instead it is broken by mountains and valleys.

This is called topography and is measured with respect to

sea level (sea level is considered 0). Our planet varies

from 0 to 1 km above sea level and 4 to 5 km below sea

level. This topography was created by forces acting in the

Earths depths.

The Earth’s density gave the first clue to the different

layers in the interior of the earth. Our planets volume was

known by knowing its radius (πr2) discovered in 250 BC. Its density was calculated in 1789 by from

the force of gravity that pulls objects to the surface. A German physicist Emil Wechert knew that

the average crustal rock like granite had a density of

2.7g/cm
3
. The planets density was measured at

5.5g/cm
3
. The heaviest rocks found on the planet was

found to be rich in iron and brought to the surface by

volcanoes. It only had a density of 3.5g/cm3.

He looked down at his feet and proposed an idea that would explain this difference. He knew

that some meteorites were a mixture of two heavy atoms, nickel and iron (density of 8g/cm
3
). If the

outer portion of the planet was light then the inner portion must be composed of the heavier

materials. The idea of a light crust on the planet surrounding a heavier core was proven by

examining the seismographs to see if there were changes in the waves as they passed into the earth.

This theory was proven correct in 1906 by Englishman Robert Oldham with the use of seismic

waves. There are two seismic waves that can penetrate the body of the planet. One of these waves

can penetrate both solids and liquids, the other only through liquid. (assignment 1,

http://www.classzone.com/books/earth_science/terc/content/investigations/es0402/es0402page0

1.cfm) By noting the missing seismic wave at different seismograms he could map a liquid core. He

discovered that the fact that deep in the earth was a molten layer. Here the planet was hot enough

to melt nickel and iron but not silicate based rocks. This explained the discrepancies in mass.

Prior to this was discovered another phenomena- the Moho Discontinuety. This was a change in

seismic wave speed as it entered the earth’s depths. Seismic waves travel slower in less dense

material. Our crust was made up of material that is less dense then the material beneath it. This

outer material, the mantel, is made up of minerals containing magnesium and iron, while the crust

minerals were mainly made up of silicate mineral composed of potassium and aluminum. Our crust

was surrounding a much denser material and our continents were found to “float” one this denser

mantle.

Courtesy of the cold war and seismic stations spread throughout the world (to monitor nuclear

testing) all of the major Earth layers had been discovered. The composition of these layers was

estimated by their densities. This density was determined by the change in speeds of the seismic

waves. Look at the figure on page 41 to see what makes up our planet. These are the main

elements that compose the planets with the other elements being present in trace amounts.

Our planet then is constantly changing under the influence of two “engines”. The internal engine

is powered by the internal heat from our planet. The external or surface of our planet is powered by

the Sun. The combination of these two driving forces comprises the Earth system. This system is an

open ended system exchanging mass and energy within itself and with its surrounding

Solar energy powers our weather creating weathering and erosion of the earth’s surface and

powers the growth of plants. Our climate is controlled by a balance of solar energy and the energy

of Earth radiates back into space. Mass is exchanged back and forth between Earth and space. We

get mass from meteors. In fact our planets origin is as an assembly of small bodies such as meteors,

asteroids and comets. The Earth, in turn, loses molecules such as water escape into space.

Earth is divided into spheres. The external spheres are energized by solar radiation. The external

spheres are the following: 1. atmosphere, 2.hydrosphere, 3. cryosphere, 4. biosphere. The internal

spheres are the following: 1. lithosphere (rock layer)

composed of the upper ridged mantel and the crust, 2.

asthenosphere or plastic sphere, 3. deep mantel, 4.

inner and outer core.

The last two spheres the deep mantel and the core

form the Geodynamo System. This system controls the

magnetic field. The first two internal spheres control

the formation of new sea floors, new land masses,

mountains and can increase the sea level. These

processes explain the phenomena known as Plate

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http://www.classzone.com/books/earth_science/terc/content/investigations/es0402/es0402page01.cfm

Tectonics.

The magnetic field is formed by the heat transfer from the inner core to the outer core which

creates convection currents in the outer core. The rapid motions from the currents stir the liquid

inner core up and electric currents form in the liquid outer core. The magnetic fields create both the

north magnetic pole which is off the earth’s axis by 11 degrees and the South Pole. This magnetic

field protects us from solar radiation. This increase radiation would increase cancers in adults, kill

phytoplankton, and injure all life forms. The interesting thing about this is that this field reverses

itself every tens of thousands to millions of years. There is no full extinction event seen at these

reversals.

Plate tectonics is driven by the internal heat, just as the geodynamo. Here the heat passes up

from the inner core, through the lower mantel to the asthenosphere. This plastic layer

(asthenosphere) develops convection currents that splits the lithosphere. It also causes volcanoes

and earthquakes while building land masses and destroying sea floor. The mountains that where

created impacts the uppers spheres, areas of the atmosphere, hydrosphere, cryosphere and

biosphere. The formation of new sea floor and its destruction impacts the biosphere and

hydrosphere.

Instead of going straight to plate tectonics I choose to lecture on rocks and minerals because

these are what we, the geologist, study to get a better understanding of the Earth. Minerals are the

building blocks of rocks. They are naturally occurring solid crystalline substance, usually inorganic

with a specific chemical composition. Minerals cannot be divided mechanically into smaller

components without losing their properties (you go down to the ions that compose them).

These characteristics that define what a mineral is can be easily explained. Naturally occurring

minerals means that these can’t be “man-made” but found in nature. Solid crystalline substance,

minerals are neither liquid or gas but a solid. Crystalline means that atoms that compose the mineral are

arranged in orderly repeating three dimensional arrays. This website will demonstrate this principle.

http://www.classzone.com/books/earth_science/terc/content/investigations/es0506/es0506page

02.cfm . Solid materials without this atomic arrangement are called glassy or amorphous and are not

minerals. Glass is such a thing either naturally occurring or windowpane. The “usually” inorganic means

that there is no organic carbon bonds as if sound in organisms living or dead. Minerals may be secreted

by organisms. Shells such as those in clams and oysters are composed of the mineral calcite. Specific

chemical composition is defined as the chemical formula that allows for only small variation that is

defined by a fixed ratio. The ratio never varies. For example olivine is composed of iron, magnesium,

oxygen and silicon and has a fixed ratio. The number of iron and magnesium may vary but the number

of those two atoms together compared to silicon atoms can’t.

The structure of mater is defined by its smallest unit that retains the physical and chemical

properties of an element. This is the atom. By this time in your education you should be aware of what

an atom is and how bonds form. Review this be reading pages 78-80 in your text book.

The crystalline structures are determined by how the anions are arranged and how the cations fit

between them. A cation’s size allows for substitutions in the mineral matrix. This size similarity creates

the variation as talked about in the chemical composition of minerals. Crystallization can occur as the

different ions order themselves during either the cooling of molten magma or during evaporation as the

ions are brought closer and closer together

Large crystals in magma grow by slow temperature changes. As the temperatures in magma drops

ions slow their movement and now can bond together and hold. If the temperature drops slowly crystals

grow larger and larger, also if the pressure increases ions are forced together crystals will also form. If

the temperature slows to fast then the ions either can’t bond together and an amorphous material is

formed. If the temperature is slow enough to allow small crystals to grow then the material may or may

http://www.classzone.com/books/earth_science/terc/content/investigations/es0506/es0506page02.cfm

http://www.classzone.com/books/earth_science/terc/content/investigations/es0506/es0506page02.cfm

not have easily visible crystals.

Crystals will form “faces”. These are the boundaries of the natural repeat surfaces. So the crystal

faces are the external expression of the minerals internal

atomic structure. Since the shape of the crystals is partially

determined by the chemical formula crystal shape can be

used to identify different minerals. Different pressures

and

temperatures will impact the shape and therefore the

properties of the mineral. This creates polymorphs,

minerals with the same chemical formula but different

shapes and different properties. An example of this is

graphite and diamond. Both are made completely

inorganic carbon. Their properties are very different.

Physical properties of minerals are how we identify

them and are determined by both their chemical make-up

and their crystal shape. Covalent bonds are stronger then

ionic bonds, giving different properties. The shape of the

crystal is determined by the different bonds. The

properties that are determined by this are the following: 1.

hardness, 2. cleavage, 3. fracture, 4. luster, 5. density, 6. chemical habit and to a lesser extent and 7.

color.

Hardness is the measure of the ease with which the surface of a mineral can be scratched. To

determine this property a scale of hardness was developed called the Mohs Scale of Hardness. It used

minerals with the softest being talc and the hardest being diamond. Of course geologist won’t carry

valuable minerals in the field so we carry simple common things such as our fingernails, copper coins,

knife blade, window glass and steel file.

Within groups of minerals there can be variation in

hardness. Hardness can also be related to other factors that also

increase the bond strength therefore the strength of the

minerals. These other factors are size, charge and packing of

atoms or ions. Size of the ions plays a major role, the smaller

the ions, the smaller the distance between them and the

greater the attraction and thus the bond. The charge of the ion

determines the attraction between them and therefore, the

strength or hardness of the mineral. Packing of the atoms or

ions refers to the amount of “space” between the ions of a

crystal the smaller the distance between the ions the stronger

the bond in the crystal.

Cleavage is the tendency of crystals to break along where

there is less bond strength. It varies inversely with the bond strength and varies along the different

planes of the crystal. Diamonds have covalent bonds, the strongest that there are. They can cleave along

specific planes along weaker planer surfaces giving perfect flat (planer) surfaces. This cleavage helps

identify the minerals. There is also different cleavage strengths. While some minerals have perfect

smooth cleavage along certain planes others have imperfect or fair cleavage. So minerals can be

assessed by how it splits apart, making specific angles. So minerals can have perfect, good or fair

cleavage. Some minerals have no cleavage what so ever. Instead they fracture because their bonds are

too strong. All minerals will fracture if struck along bond strengths that are distributed along cut across

cleavage planes. Fractures may be conchoidal, showing smooth curved surfaces (like a bullet in hole in

glass), another common fracture surface has the appearance like split wood. This gives a fibrous or

splintery appearance. Again the shapes and appearances of fractures depend on the crystal structure

and composition. This is an excellent website for different cleavages and mineral examples

http://www.rockhounds.com/rockshop/xtal/part3.shtml

Luster is how the surface of a mineral reflects light. Luster is controlled by the kinds of atoms and

http://www.rockhounds.com/rockshop/xtal/part3.shtml

the type of bonds that the minerals have. The crystal structure impacts how the light passes through the

minerals. Ionically bonded crystals tend to have a glassy or vitreous luster. Covalently bonded materials

vary more. Many have adamantine luster like diamond (think sparkle). Metallic lusters are often shown

in pure metals like gold, and copper. Sulfides often have metallic luster. A pearly luster is imparted

minerals as light passes through a clear surface and reflected back from other crystal planes beneath the

surface. This website will demonstrate crystal

luster http://dph1701.tripod.com/geology/properties/luster.html

Density depends on the atomic mass of a mineral’s ions. It is also dependent on the amount of

space between the ions. The closer the ions are packed together in a crystal the more it will “weigh”.

Increases in density caused by pressure will impact how a mineral will transmit light, heat and seismic

waves. This change with density explains how we can use seismic waves to judge the make up of the

interior of the earth.

Color is an elusive property. It is determined by the presence of certain ions in a mineral. The mineral

called olivine has a formula (Fe,Mg)2SiO4. The Iron and Magnesium

cations are similar in size and often form a mixture in the olivine

crystal. If there is only Iron (Fe) present the green since iron reflects all

light except green. If it only has magnesium (Mg) it is colorless. The

mixture of the iron and magnesium make olivine vary in color. This

would indicate that color is a good way to identify a mineral. The

problem happens when there are impurities incorporated into the

mineral. These are called trace elements. An example of this is the

mineral corundum (aluminum oxide). If there is a small amount of

chromium in it we have a ruby. If there is either titanium or iron we have a sapphire.

Streak is a subset of color as well as an indication of hardness. Unglazed porcelain will remove

molecular level crystals are reveal the true nature of a mineral. A classic example of this is the mineral

Iron Pyrite or fool’s gold (FeS2). This mineral is gold inn color and often confused early miners and

hobbyist into thinking that they had found gold. When rubbed across a streak plate instead of leaving

behind a gold streak like true gold would it leaves a black streak.

The last property is crystal habit. This is the shape that and individual crystal or aggregate of crystals

will form. It is diagnostic for some minerals such as quartz which has a distinctive 6 sided column topped

by a 6 sided pyramid like structure. This is dependent on the of ions in the crystals structure. Many

minerals can have more than one habit. An example of this is gypsum- try to find examples of gypsums

different habits.

Unique properties- some minerals have unique properties that can be used to identify them that are

dependent on their chemical formulas. Calcite with the formula of CaCO3 fizzes the presence of acid.

Dolomite, Ca,Mg(CO3)2 must be powdered to fizz. Your clay minerals are plastic when wet and smells

earthy. One group of clay minerals will swell when wet causing tremendous problems in engineering.

There are approximately 30 rock forming minerals that are the building blocks of our planets. Many

http://dph1701.tripod.com/geology/properties/luster.html

of the other minerals occur in veins or form secondarily and are important for providing raw materials

such as copper, rare earth elements, tin etc. The 30 minerals reflect the 8 most common elements that

make up 99% of the Earth’s crust.

The most common of the mineral groups is the silicate group. This group is characterized by the

silicate tetrahedron. Here the silicon ion (Si
4+

) is surrounded by four oxygen (O
2-

). The fact that the

oxygen share charges creates an amazing strong structure. The Si with 4+ is balanced by the four O
2-

so

is neutral. This allows the oxygen with their shared negative charge with a free charge of 1- to bond with

other cations or it the oxygen can be shared with other silicate tetrahedrons.

There are four forms of silicate minerals that

are common as rock forming minerals. They are

the following: 1. Neosilicate, a single silicate

tetrahedren bonded to a cation, 2. Inosilicate,

here a chain of tetrahedrons forms. This chain

can either be a single chain such as the pyroxene

group or a double chain such as amphibole, 3.

Phyllosilicates or sheet silicates here the crystal

growth form thin sheets along one plane

examples of this are the micas (a secondary

mineral formed from micas are the clays and

shares the same structure), and 4. Tectosilicates

(framework) are the complex forms that have a

three dimensional framework. Rocks can have

two types of tectosilicates, one is quartz with no

cleavage planes and feldspars which have two

planes at right angles. While quartz is only made

up of SiO2 other silicates are bonded to cations

such as sodium, potassium, calcium, magnesium

and iron. There can be cation substitution for the

silicon by aluminum in the silicate tetrahedron.

Carbonates are those minerals that combine with the anion complex CO3
2-

. It is probably the second

most second common mineral family in

the Earth’s crust. Carbonates have one

carbon surrounded by three oxygen

giving the group a negative 2 charge.

This group combines with calcium (Ca
2+

)

to give calcite (CaCO3). This forms the

rock limestone. When magnesium

combines with calcium we have the rock

forming mineral dolomite Ca,Mg(CO3)2.

Other carbonates provide valuable

minerals such as copper from MALACHITE, Cu2(CO3)(OH)2 and AZURITE, Cu3(CO3)2(OH)2. Malachite is

green and Azurite is blue

Oxides are minerals formed by oxygen combined with metallic cations such as iron, both Fe
2+

and

Fe
3+

. This group is an important source of ores. Three iron minerals are commonly found in crustal rocks.

The first is magnetite (Fe3O4). This mineral is important not only for ore but in proving an important

geologic theory of plate tectonics and is the source of magnets.

Hematite

(Fe2O3) is a major source of iron ore and an indication of the formation of free

oxygen in our own atmosphere for the first time. It can be seen as a

semiprecious jewel and as the red stain in many soils and as yellow stain in

others. Goethite (limonite) is a hydrated iron oxide FeO(OH).

Sulfides are minerals in which the sulfide anoin S
2-

combining with metallic

cations. Most of these compounds like metals and are a valuable source for

metals that we have used for centuries. Iron pyrite (fool’s gold) is a FeS2 and Galina, (PbS) a major

source of lead and our state mineral.

Sulfates are a tetrahedron with the sulfur surrounded by four oxygen (SO4
2-

). Gypsum that makes up

wallboard, is an evaporite mineral (CaSO4.2H2O). The pure form is anhydrate and the water is missing

from the formula. Sulfate minerals were found as an evaporite from water. We found sulfates on the

surface of Mars, one more indication that Mars was once a water world like Earth early in its history.

Another group of minerals are the Halides. These minerals are evaporites like gypsum. An example

of a halide is halite also known as salt (NaCl). This and sylvite (KCl) can be found in sedimentary rocks.

These deposits often have oil in them since they are porous.

Rock is a naturally occurring solid aggregate of minerals or in special gases nonmineral solid matter.

Concrete may have rocks in it and may look like a type of rock but it is not rock! The minerals in rocks

are joined together in such a way that their individual properties remain. There are three types of rocks:

1. igneous rook formed from solidified molten material (magma), 2. sedimentary rocks made from loose

particles that have been cemented together or made from ions the combine in water to form new

minerals that are cemented together, 3. metamorphic rock is rocks that have undergone temperature

and pressure change. We will be looking at each class of rock and how they form in full chapters later in

this book. Below is an overview of the rock types.

Igneous rocks are associated with molten material. This material can be from the mantel or

melted crust material. Texture, iron content and silica content determine the type of igneous rock. The

texture determines the cooling temperature. Rapid cooling gives small to no crystal formation. This

means that the rock formed on the surface. The main minerals for igneous rocks are quartz, feldspar,

mica pyroxene amphibole and olivine. Mantel rock will have mainly olivine, and pyroxene. Melted

crustal rock has large amounts of quartz in it. Texture is a clue to the environment, internal (intrusive) or

external (extrusive). This was known for 200 years and later confirmed with the developing of polarizing

microscope and the careful grinding of a rock thin section (ground rock so thin light can pass through it).

Texture is created by cooling temperatures. Ions in hot magma have too much energy to bond together

Hematite

and form a crystal. As cooling proceeds the ions lose energy and can then form crystals. Pressure will

also help in this since it forces ions together regardless of the heat energy. If the cooling proceeds slowly

as in intrusive material you have large crystals, if ejected into the surface you get small crystals or no

crystals.

Intrusive rocks are coarse textured (phanorytic.) These rocks

have slow cooling regimes cooling over thousands and thousands of

years in the crust of our planet. The heat is held in by the overlaying

rock. Elephant rocks in Missouri are a perfect example of such a rock.

This is an igneous intrusive body injected into the crust over a billion of

years ago.

Extrusive rocks have different types of appearances, one composed of

fine grained aphenitic another by glassy (no crystals) rocks. These categories

are dependent on how they erupted from the volcanoes. Lavas have a range

of appearances dependent on their chemical make-up and temperature.

Pyroclastic formation is characterized by violent

eruption with lava thrown into high into the air. If

the material is ejected rapidly and cools rapidly it forms volcanic glass- mineral

free since amorphous. Pumice is a form of igneous rock that forms from

volcanic glass with air pockets or vesicles. These vesicles are formed by the

degassing of the molten material (CO2, H2O, etc.). Volcanic ash is composed of

fragmented rocks, lavas and/or volcanic glass. It is thrown high in the air and

smaller fragments will travel around the globe. Bombs have a range of shapes and made up of solidified

lava. They are tossed into the air and fall along the sides of the volcanic cone. The last two are scoria and

pumice. These are gas filed lava. Pumice (to the left) is so light that it floats.

There is one more texture, a mixed texture indicating two different cooling regimes. This is

called porphyritic texture or porphyry. Here a slow cooling regime starts and

large visible crystals form. These are then there is a volcanic eruption before

more large crystals can grow and this gives us the two different crystal types.

Igneous material is also classified by chemical content. We break the material

into four types according to the proportion of silicate minerals. Specific

minerals form at specific temperatures. Minerals with a high proportion of

iron and magnesium and calcium compared to silica form this group and are

called mafic from magnesium. The mafic and felsic mineral suites are on page 112 in your book. The

feldspar group is divided into potassium rich (orthoclase),

sodium rich plagioclase and calcium rich plagioclase. The last

two the sodium and the calcium are end the members of a solid

solution where the plagioclase formula is NaAlSi3O8;CaAl2Si2O8.

The more calcium in the plagioclase the more mafic the forming

rock and the higher the melting temperature to the right is an

Labradorite- tectosilicate

– Ca(50-70%) Na(50-30%) (Al, Si)AlSi2 O8

example of these mixture. The more sodium, the more felsic the magma melt and the lighter the

igneous rock( look at the chart on page 113).

Mafic Rocks a have large amounts of olivine and pyroxenes giving the rocks their characteristic

dark colors. There may be a small to moderate amount of calcium plagioclase. The lava form of this is

called basalt. There are several areas of sheets of basalt such the Columbian Plateau along the Columbia

River in Washington. India as an even larger area, the Deccan Traps, where kilometers thick layers of

basalt contributed to the Cretaceous extinction event and another in Siberia with an area as large if not

larger also associated with an extinction event (Permian).

There is another mafic rock form. This form is called ultra-mafic. The mineral suite is primarily

made up of olivine with a small amount of pyroxene. This is the material that makes up the upper

mantel. The basalt upwelling at the spreading centers formed the ocean crust.

Felsic Rocks are poor in iron and magnesium. They are also poor in calcium. These rocks tend to

be light in color and one of the most abundant intrusive igneous rocks. They contain approximately 70%

silica and are abundant in quartz and orthoclase feldspar with some

sodium feldspar (albeit minerals). The intrusive form of this igneous

rock is Granite, the extrusive form is Rhyolite. These rocks can appear

as light brown, salt and pepper, pink, or orange or in some cases

almost purple (Missouri rhyolite). The Picture on the left is an image of

this rhyolite. Notice that it is porphyritic.

Between

the end members

of these two rock

types are the rocks

that are called the

intermediate.

These rocks have

less silica then the

felsic and more

than the mafic.

They have some

quartz, micas and

may have some pyroxene. They may also have amphiboles. The intermediate is divided into

granodiorite and diorite. Granodiortite is very difficult to differentiate from granite. This is done by

looking at difference in the percentages of quartz, orthoclase and sodium plagioclase. We will then only

talk about diorite and its extrusive form andesite. This material has a mineral suite with pyroxene like

mafic and calcium plagioclase but it also has amphiboles, micas, a mix of the sodium/calcium plagioclase

minerals and some quartz. The variation in the amount of silica gives its melt a variety of properties that

can swing from one extreme to another. The last is the composition factor impacting the melting is the

chemical formula. The more mafic the melt, the higher the melting temperature for mineral formation

and mafic melts are characterized by less silica in the melt and more iron and magnesium. Conversely

the more felsic the melt represented by more silica, the lower the melting temperature.

Sedimentary Rocks

Sedimentary rocks formed from the breakdown of other rocks by surface processes. There are

two types of weathering, physical and chemical. These processes seldom occur alone but are combined.

One type of weathering can dominate depending on the climate.

Physical weathering takes place without the modification of the minerals of the parent rock, it is

a mechanical process. So how does the rock break down? The first method is abrasion. Here a small

fragment of rock strikes the surface of the rock and knocks chips off of the parent rock. These particles

can be transported by air or water. In desert situations the particles transported by wind are silt size and

fine sand size in origin. In water currents can transport smaller

particles and larger ones depending on flow. Think about

sandblasting, wind is dry sand blasting and water is wet sanding.

Abrasion is just one method. Tree roots expand and

contract as water flows through them and is pumped up to leaves

during photosynthesis and stops during respiration. This continued

expansion and contraction fractures boulders. Another form of

physical weathering is frost wedging. You can see this along I55.

Water percolates into cracks during the day in winter. It freezes at

night and expands, fracturing the rocks. Another method of

fracturing rock is heat exchange. During fires a rocks outer surface

expands while the center remains cool for a time. This creates

stresses that can start cracking the rock when the rock cools the

reverse takes place. Here the surface cools over the hotter expanded inner core of the rock.

Chemical weathering takes both heat and water to take place. Heat is necessary for a chemical

reaction to take place and water allows for the ions in minerals to reconfigure into new minerals.

Feldspars can become clays and so can mica. The chemical reaction releases extra silica ions (H4Si4, silicic

acid) that react with water to precipitate out quartz. The amount of water controls the amount of

weathering at a given time (deserts have chemical weathering from dew). The necessity for heat should

tell you that during winter and in cold climates when water is frozen suspends chemical weathering.

Physical and chemical weathering takes place together for the most part. As rocks are broken

down physically more surface area is exposed. This gives more area for chemical weathering to take

place speeding the breakdown of the initial rock and new minerals forming. Smaller particles have

greater surface area to react with the environment.

Transport

This break down produces sediment that is transported to and deposited in low lying areas.

Physically weathered particles are often angled but as they are transported they become progressively

more rounded. This will give clues as to the amount of transportation. Wind transport has very round

particles and they are often frosted from impact with other grains. Clues of the amount of time spent in

transport comes from the particles are well sorted or not. This means that how many different types of

minerals are present. Mature sediment is predominantly quartz in nature since quartz resist chemical

weathering.

Deposition

Once transport is done there is

deposition. This is the time when the velocity

of the transporting media drops to the point

that a particular sized can it can no longer be

carried. When the particles settle out they

settle in roughly horizontal beds. In water

particles can settle out also new minerals form

as ions recombine and settle out.

Burial takes place as layer after layer

of sediment are deposited. This often takes

place in basins. These sediments will remain in the basins until plate tectonics either causes an uplift or

the crust is recycled down in an area of subduction. The burial leads to compaction.

Diagenisis

Diagenisis is the change of sediment into rock. This is also called lithification. The first step in

this is compaction. Here spaces found between the grains of sediment are narrowed. As compaction

proceeds the amount of water that is present in the pore spaces is reduced. This is followed by

cementation. The cement can very and this variation changes the strength of the rock. Cements are

formed by chemical weathering making new compounds. Calcium carbonate is often present in rocks

formed either in shallow ocean basins or in the desert (calcium carbonate is present as any water

evaporates in a desert environment). This cement will dissolve away in the presence of acid (rain water

is a pH 5 and that is without the addition of acids from coal burning). Another cement is hematite, Fe2O6.

This cement is far stronger and the rocks cemented by it will hold up even in the presence of acids of

many acids. Clay is also cement. Clay minerals can be formed by water interacting feldspars and micas.

SiO2 is the strongest cement of all. It is formed by chemical weathering feldspar rich rocks and micas.

Sedimentary rocks are broken down into two types, clastic or siliciclastic and chemical including

biogenic. The clastic rocks are further divided by grain size. Course grained rocks are made up of gravels.

Gravels can range from 2mm (dry pea sized) to larger than 256 mm (diameter of over 7 feet). The

medium grain or sand size has a range of 2-0.062mm (dry pea to granulated sugar). Fine grained size

ranges from 0.062-0.0039mm (granulated sugar to flour) and makes up mud and silt. The finest grain

size is 0.0039 or clay size. This size feels “soapy” when rubbed between your fingers.

The gravels form the rocks conglomerates or breccias. A conglomerate is made up of rounded

grains while a breccia is made up of angular grains. The angulation tells

ou about the distance from the source that the grains have traveled. A

breccia has undergone lithification close to the source, possibly from

the talus at the bottom of a mountain. A conglomerate has traveled

further from the source

becoming more rounded.

The size of a conglomerate’s

grains tells you the strength

of the current that transported them. The grain size of the

conglomerate is not uniform but made up of many different

sizes with the largest being gravel sized.

The medium sized material makes up sandstone.

This can be divided into fine, medium and coarse. A sandstone that is made up predominantly of

medium to fine particles is well sorted an indication of the current strength or wind strength since the

larger particles drop out with the drop in velocity. The sandstone is also graded according to the degree

of roundness. The more round the particles in the sandstone the further the transport from the source

of the grains. The last classification is maturity. If the sandstone is made up of only one type of grain,

quartz, it is called mature and is called a quartz

sandstone. This type of sandstone indicates chemical

weathering and time. All other grains minerals will

breakdown to quartz given enough time. The white

sandstone bluffs along I55 are an example of this. If

there are pebbles (rock fragments) this is called lithic

sandstone. If there are feldspar minerals present it is

an arkrose sandstone ? Greywacke is sandstone that is

mixed with clay. This can be seen in tidal flats and

floodplains.

Clays and silts make siltstone, mudstone and shale. The sources of these sediments and stones

can be lakes, floodplains and the abyssal plain of the ocean. Siltstone and mudstone are thick and blocky

while shale has fine partings making thin layers. When the shale is black it indicates that it is rich in

organic matter and was formed in an anoxic environment. This is the shale that is being “fracked” or

fractured to retrieve the oil and natural gas that is trapped in it.

Chemical and Biological Rocks

Chemical and biological rocks are by products of chemical

weathering. Ions produced by the chemical weathering of different

minerals are recombined to form new minerals. The biological

rocks have animal or plants combining these ions to produce new

minerals that they use for their shells or support structures

(calcareous algae). The ions that biota chooses for their shells determines the raw material available to

form rocks. If CaCO3 is chosen then limestone is formed. If SiO2 is chosen (diatoms) you get a siliceous

sediment and chert is formed. There is another form of biological rock and that is made from plant

material and these are not forming new minerals. Here plant and animal material deposited in swamps

undergoes diagenisis to form coal.

Chemical precipitates forms in water that are saturated in ions. This can take place due to

evaporation found arid environments. Water as it evaporates will

precipitate out first CaCO3, then gypsum (CaSO4), halite (NCl) and

finally silvite (KCl). This forms a ring system with the least soluble

coming out first followed by next less soluble and so on. There is

some mixing between layers; it’s not perfect rings but mix at the

margins. The gypsum forms rock gypsum and the NCl and KCl forms

rock salt.

Limestone or CaCO3 can directly form out of seawater. Ca
2+

in warm seawater will directly combine with CO3
2-

to form CaCO3 or

lime muds. These muds undergo diagenisis forming limestone.

Limestone formed this way can be used to predict a paleoclimate

and plate tectonic activity.

Another rock formed as a precipitate is phosphorite. This rock forms from the breaking down

and release of phosphates from bone and teeth or from hydrothermal vents and weathered igneous

rocks that have phosphate bearing minerals in them.

A modification of limestone is dolomite. Here percolating ground water seeps down through the

rock and magnesium combines with the limestone. It formula is CaMg(CO3)2. While this stone is more

resistant to acids therefore acid rain it is not prized for cement manufacturing and for greenhouse gas

release. Concrete is made from CaCO3 and one CO2 is released in the process. To get the same amount

of CaO for concrete you release twice

as much CO2.

Metamorphic Rocks

Metamorphism is change in

form in response to changes in

temperature and pressure. This

change takes place in the mineral

content of the rock, but it happens in a

solid form and is due to plate

tectonics. By saying this it is implied

that metamorphism takes place at

plate boundaries but that is not totally

true. One form takes place in basins

were sediment is deposited and undergoes increasing pressure at depth.

As different events come to play different states of metamorphism comes to play. An example

of this progression of one form changing into another is below. Yet despite

these changes there is a preservation of their former conditions and the events led to metamorphism in

the minerals that have formed. The image above shows not only a change in particle size with increase

degree of metamorphism but a change in the mineral composition of these rocks. These changes are still

limited by the source rock. Chemical rocks with only one mineral present such as limestone and chert

are restricted in the metamorphic rocks that they can become.

In the process of metamorphism temperature plays a crucial role. As plate tectonics moves the

sediment from the surface to depth there is an increase in temperature (30oC/Km depth). The rocks

adjust to these higher temperatures by recrystallizing. Each mineral is stable at a specific temperature.

We use this information as a geothermometer to reveal the temperature at which the rock formed.

Remember when we talk about stability we are not talking about an immediate change but a geologic

time frame. You can observe high temperature minerals on the surface. These minerals will change at a

faster rate than low temperature minerals. An example is olivine. This mineral will break down to

limonite if exposed to humid climates in a few decades.

Pressure also affects the rocks during metamorphism. Here the rocks are exposed to two types of

pressure, confining and directed pressure. Confining pressure is a pressure that is all around you. You

are surrounded by ~1atm pressure as you read this. If you dive in the ocean the pressure increases

around your entire body until you’re crushed like a crushed bear can. Confining pressure increases with

depth of the Earth.

Directional pressure is forces directed in a particular

direction. This is called differential stress and is

concentrated along discrete planes. Heat softens the rock

and the directional pressures causes severe folding.

Minerals maybe compressed elongated or rotated.

These directional pressures create different textures. The

minerals oriented perpendicular to the forces form

foliation, a set of wavy parallel cleavage planes. This texture is formed by the platy minerals such as the

micas. Metamorphic rocks are classed according to four main criteria, the metamorphic grade, crystal

size, type of foliation and banding.

Fluids have a major role in metamorphism. The source of the water is hydrothermal and introduced

to the depths by water saturated minerals such as clays in convergent plate boundaries and from cracks

in the crust that let surface waters inter the depths of the lithosphere. The fluids bring CO2 and other

substances such as gold copper and silver into contact with the rocks minerals. This allows for

metasomatism or change in the rocks composition by these fluids.

This metasomatism may be the reason for granoblasitic rocks. These are rocks that are

nonfoilated with crystals that are equidimensional in shapes such as spheres or cubes. Examples of this

are marble and quartzite. Here the existing crystals have be altered, increasing in size and intergrowing.

Quartzite, formed from sandstone, is some of the hardest and most weathering resistant rock known.

The last thing I will mention is that

any rock can form any other rock. All

rocks undergo erosion deposition

and lithification. Any rock can

undergo temperature and pressure

change forming a new metamorphic

rock and any rock can melt and cool

forming a new igneous rock.

This will cover how Geologist Study the Earth, Plate Tectonics and Minerals. It is composed of 5 short answer questions, 5 matching and 10 true/false

You should know what determines a mineral and how minerals are identified (think of your experiences in lab)

There are examples of minerals for each mineral class, you should know them. Again this is lecture and lab.

There are proofs of plate tectonics both from Alfred Wagner and from later. You should know them. The later ones you should be able to explain them and how they are formed and what minerals might be involved.

You should know the parts of the different plate boundaries.

You have been given multiple examples of plate boundaries and steps in divergence, you should know them.

You should know the spheres of our planet, both inner and outer and how they interact and what powers them.

There is a guiding principle in science, you should know this principle for proving theories of science and how it has to be modified for geology.

There is a guiding principle in geology that describes how the process of the earth works over time, you should know this.

Plate Tectonics is the driving force of geologic structures that shape the world that we live in. The

first indication that continents might have been linked physically took place as soon as there was

mapping. It was known by the sixteenth and seventeenth century that the continents fitted together like

pieces of a puzzle. This and other proofs listed below lead to the concept of continental drift, that the

large continents had once been linked together. The scale movements of continents across the across

the surface of the planet was mind boggling.

By the close of the nineteenth century the geologist Edward Suess postulated that the southern

continents were joined together. This was from evidence seen by fossil animal distribution. Ancient life

forms have ranges just as modern animals. Tigers are found in India and Siberia, not in North America.

These ancient animals couldn’t get from South America to Africa, from Antarctica to Australia to India.

There were rock layers both sedimentary and igneous that were continuous on all of the five continents.

He christened this large continent Gondwanaland.

In 1915 Alfred Wegener wrote a book on continental drift. He proposed another super continent

called Pangaea. This continent included all of the modern continents. His mechanism for the movement

of the continents was that the continents moved through ocean crust, drifting until they joined then

breaking apart again. Wegener and others argued for their evidence pointing out rock similarities

type, similarities in rock trends and ages using all of the information gathered from Steno’s laws and

fossil assemblages. They also showed that certain distant continents had similar plants and animals that

entered a different evolutionary path after the continents separated. An example of this is the fresh

water fish the Arowana found in both South America and Australia. Another example of this is the large

amount of marsupial

fossils found in South

America and Australia.

Placental mammals

were the dominant

mammalian life forms

in Eurasia, North

America and Africa.

Only in South America

and Australia were

marsupial fossils

dominated. It wasn’t

until 3 million years ago

North and South

America joined

allowing placental

mammals to gain

dominance in South America. Despite this evidence Wegener and his followers mechanism for

continental movement was badly flawed. They proposed that the tidal forces from the Sun and Moon

like the tides in the ocean. This force is much too weak to move a continent so the theory was rejected.

Fossil plants and animal distribution on southern continents

In 1928 a geologist Arthur Holmes proposed the convection currents split the continents and that

these currents were in the mantel. Remember the knowledge of a mantel was already known at this

time. Ironically this was a mechanism had been proposed by Benjamin Franklin in 1782. Many

geologists argued against this and Holmes bowed to their criticism.

It wasn’t until WWII that there was evidence to

show that Holmes (and Franklin) was correct. A

marine geologist, pioneer of marine seismology,

deep ocean photography by the name of Doc Ewing

found that the sea floor was composed of young

basalt, not old granite (we knew absolute age

dating this time) as originally thought. The other

finding was that there was mapping of the

undersea Mid-Atlantic Ridge. In the center of this

ridge was a rift valley. These were mapped by

Marie Tharp and Bruce Heezen. It was found that

the rift was and active feature with volcanic activity

as well as seismic activity. Harry Hess and Robert

Dietz proposed that the Earth’s crust separates

along the rifts and forms new oceanic crust.

At this point in time many thought the Earth was continuously expanding. It took a massive

earthquake (1964 Alaskan Earthquake) to show the destruction of the ocean floor. Here a large portion

of the seafloor moved beneath the Alaskan crust. In 1965 J. Wilson proposed the theory of plate

tectonics. That seafloor was recycled down deep trenches and at these regions there were earthquakes

and volcanoes. This movement explained the rock folds and faults. It also explained many of the

minerals. It was also shown that the rates and directions of movements of crustal rocks were

mathematically consistent. Wilson the proposed plate boundaries. There are three of them, divergence,

convergence and transform.

Divergence, found in the Mid-Continent Rifts, created the new seafloor, calling it seafloor

spreading. Mantel temperature difference drives this. A plume of heat or possible actual upwelling

mantel moves upward to the plastic asthenosphere. Here convection currents developed. The

asthenosphere drags against the lithosphere splitting it. New material from the asthenosphere moves

upward and forms a new ocean crust material. This happens in the rift valleys of the Mid-Continental

Rifts that bisect the ocean floor.

Rift valleys form in the center of continents forming with volcanoes and earthquakes as the continents

tear apart. This can be seen in the Great Rift Valley of East Africa creating parallel valleys. The ocean

plate if produced by basalt (iron rich and silica poor igneous rocks). The minerals found here are olivine

and pryoxine and some feldspar. When rifts are on the continent the upwelling magma first melts

continental crust so you find quartz, mica, and feldspars. An example of a continetal rift valley is the rift

valley found in Iceland. Here new Atlantic Plate is being made as North America moves away from the

Eurasin Plate. Iceland sites on top of the Mid-Atlantic Rift. Not all rifts splits continents. Instead some fail

leaving zones of weakness. An example of this is our own New Madrid Seismic Zone as well as the

Wabash Seismic Zone. These rifts failed hundreds of millions of years ago.

There are continental rifts that you see today that have been successful. Here the rift valley continues

until new seafloor made up of basalt

forms. These flood forming a linear sea

as seen in the Gulf of California (Sea of

Cortez) and the Red Sea. At the Gulf of

California, Baja California splits off of

the North American Plate forming new

seafloor. The Red Sea is the breaking off

of the Arabian Plate from the African

Plate.

The final phase of divergence is the

expanding ocean. The upwellings have

created underwater mountain chains.

The mountain chains are split by the rift

valley where active volcanoes and

magma create new ocean floors.

Convergent boundaries are scattered

over the globe. Here plates collide and

ocean crust is recycled back into the earth for two of these boundaries. There are three convergent

plate boundaries: 1. Ocean-Ocean, 2. Ocean-Continent, 3. Continent-Continent. These convergent zones

are marked by forms of metamorphic rocks and specific minerals. They are also marked by deformation

of rock layers with folds and faults as well as volcanoes and earthquakes.

Ocean-Ocean Convergent plate boundaries has one plate descending beneath another. This is called

subduction. This event takes place along in narrow deep-sea trench. The trenches are the deepest

portion of the ocean. The some descend as deep as 11 km, an example and the deepest the Marianas

Trench of western Pacific. At this an older portion of the oceanic lithosphere sinks into the

asthenosphere and then recycled

into the mantle as the

asthenosphere convection currents

drags it down. The water from the

subducting plate is squeezed out of

the hydrated minerals and rises

into the asthenosphere. There

the water drops the melting

temperature of the asthenosphere

and this molten material creates a chain of volcanoes, an island arc. There are many examples of this,

Indonesia, Philippians, Aleutians, and Japan. Here you can find volcanoes and major earthquakes. Some

of these earthquakes are small and some huge like the magnitude 9 in 2004 at Sumatra and the recent

2011 magnitude 9 at Japan. The minerals here have undergone both mixing with ocean crust and

fractionation and are intermediate in nature.

Ocean-Continent Convergent plate boundaries have subduction again. Here the heavy iron rich ocean

lithosphere sinks beneath the silicone rich continental crust. The continental margin crumples and

deforms and uplifts rocks into mountain chains that parallels to the deep sea trench. As the oceanic

lithosphere moves beneath the continental crust lighter material is scrapped off onto the continental

crust expanding the continent.

Again the water from the hydrated

minerals melts the asthenosphere.

This material rises up and melts

continental crust. Such a boundary

can be seen at the Cascade Range.

It can also be seen in South

America were the Nazca plate dips

beneath the South American Plate

creating the Andes. This is the

location of the largest earthquake in recorded history, magnitude 9.5 in Chili in 1960 and a magnitude

9.2 in Alaska in 1964.

Continent-Continent Convergence takes place when two continents collide. This is how Pangaea and

Gondwanaland were assembled. It happens when one oceanic crust being subducted under a

continental crust has a continent on it. As the subducting plate sinks the continental crust collides and

the two continental lithospheres join. This collision doubles the thickness of the crust at this area. The

Indian and the Eurasian plates have

done just this raising up the Tibetan

Plateau and the highest mountain

range that exist today, the

Himalayan Mountains. Other

example of this is the Alps, and the

Pyrenees Mountains. In the past the

continuous collisions from 440 to

approximately 300 million years ago

formed the Appalachian Mountains on our own continent.

The last boundary is the Transform-Fault Boundary. These boundaries are normally associated with

divergent plate boundaries. They offset the Mid-Oceanic Ridge and allow for differences in magmatic

upwellings. In certain areas this boundary can be found on continents. One such area is the San Andreas

Fault in California and the Anotoli Fault in Turkey. Both have been sites of major earthquakes and

thousands of deaths. Notice there are no volcanoes associated with this plate boundary.

Plates are normally bounded by multiple boundaries. Our plate has the Mid-Atlantic Oceanic

Ridge (divergent plate boundary) and two (or more) transform-fault plate boundary. One of these

transform-fault plate boundaries is between the North American Plate and the Carrabin Plate. This was

the location of the Haitian earthquake in 2010. The other is the transform-fault boundary between the

Pacific Plate and the North American Plate as represented by the San Andreas Fault. We also have a

transform-fault plate boundary in Canada. Our plate overrides the Pacific Plate at the Aleutian Islands

and continues to a portion of Japan (our plate is more then North America). Our plate also boarders

three different convergent plate boundaries, in the Pacific Northwest our plate override’s the Jaun de

Fuca Plate. In the country of Mexico the North American Plate overrides the Cocos Plate. We have a

junction with Eurasia that has not been identified (probably a transform-fault).

The proof of the divergence and seafloor spreading was recorded on the floor of the ocean

itself. Geologist modified the magnetometers developed to detect submarines from the magnetic fields

from their steel hulls. These modified magnetometers were sensitive the magnetic field on theocean

floor. They discovered a magnetic anomaly. The magnetic field alternated between high andlow values

in narrow parallel bands that were symmetrical with the mid-ocean ridge. The reason for the magnetic

field is the mineral magnetite. It is charged and floats free in magma until that magma cools. Once the

magma cools the magnetite will point to magnetic north. The anomaly was an increased field

alternating with a decrease in the field. The

increase in the magnetic fields is oriented

to where the magnetite points to our

magnetic north. The decrease in the field is

when the magnetite points in the opposite

direction. This reversal shows dramatic

change in the geodynamo so that the field

reversed. This stripping on the seafloor

parallels the mid-oceanic ridge. The

stripping where the field is normal or

reversed are called magnetic chroms.

When combined with absolute age dating

this was proof spreading centers.

Deep-sea drilling combined

with absolute age dating gives us the

seafloor isochroms. The youngest rock

is found at the spreading centers. The

oldest rock is found adjacent to

specific continents. The oldest rock is

180 million years old. The continents

are much much older. In our own state

the highest point, Taum Sauk

Mountain, is 1.28 billion years old. This

means that the seafloor is new and now gives credence to Wagner’s Pangaea. We can reconstruct the

plate movement by using the transform-fault plate boundaries we can deduce the movement of the

plates. The isochroms will place the continents at different points of time. Because of subduction the

original seafloor was destroyed by subduction returning to the older rock

information we can rejoin the jigsaw puzzle. Using old mountain belts such as

the Appalachians of North America and the Caledonian Mountains in

Iceland and Scotland we join North America to Europe. The fossils

magnetism of continental fragment record it ancient orientation and

magnetic latitude. This can be augmented by paleoclimate information

from the fossils and minerals. Look at the on pages 70 to 71 to see the

growth of the world as we know it and our potential future position. To

get a picture of the time it will take to get to future world here is a simple

exercise .Assignment Using the fact that the plates in Iceland are moving

apart (creating new land for Iceland) at 25mm per year how long will it take for

Iceland to grow 1 km.

Further proof of this theory of plate tectonics came with GPS (global positioning system). GPS stations

set up over continents record the changes in positions of the continents. While this gives us an accurate

measurement of the speed of the boundaries for this brief period of time it doesn’t give us changes of

plate movement over time. For that do the exercise. Here absolute time calculated by isotope decay and

position curtsy GPS can be combined to give changes in plate movement over time.

The movements of these plates are powered by our geodynamo. Convection currents upwell and to

work on the plates. There are two thoughts of for the convection currents. one proposes one current

circulating between the upper and lower mantel. The other theory is that of two convection currents.

the convection current of the lower mantel and creates a convection current in the upper mantel. The

felling at the moment is that the spreading centers are controlled in their movement by the descent of

the plate at the subduction zones. This is called slab pull ridge push causing a slow upwelling at the

spreading centers along the fracture represented by the rift valley.

There is another upwelling from the mantel. This is the mantel plume. A narrow slender cylinder of fast

rising mantel material. These areas are often far from the spreading centers. An example of mantel

plumes can be seen in the Hawaiian Islands, the Galapagos Islands and Yellowstone.