Section 2 - Rock Cycle, Minerals, Raw Materials

Rock Cycle - Lecture Notes

atom (Review) Atomic Theory

Each atom is made up of an outer shell of electrons and a heavy nucleus containing protons and neutrons.  They are referred to with the following notation

If the size of the nucleus were equivalent to a tennis ball (r~3.5cm), then the electrons would be in orbit at a distance of 1.5 km!  If this tennis ball were entirely composed of carbon atoms and had a mass of 50 grams, then it would contain about 2.5x1024 atoms or

2,500,000,000,000,000,000,000,000.0 atoms.

Compare this to the estimated number of people on the planet of 5,000,000,000.0 people.

Quantum mechanics tells us how the electrons behave in "orbit" around the nucleus.  All the chemical properties  (i.e. combine and react with other elements) of that element are governed by the "configuration" of electrons .
    Examples:  Dynamite releases stored chemical energy contained in the bonds between elements and molecules.  Plant photosynthesis occurs via a complex set of reactions involving energy, light, and chemicals.  Just about everything we encounter in everyday life is a result of chemical reactions and bonding between elements.

Composition of Natural Earth Material

Types of Chemical Bonds
    Covalent Bonding - Very strong, shares the outer shell electrons.  (e.g. Diamond)
    Ionic Bonding - One atom loses a charge (e-) and another gains one, medium strength.  (e.g. NaCl)
            ~90% of all minerals have ionic bonding
    Van Der Waals Bonding - Weakest bond, results from a slight polarization in the atoms.
    Metallic Bonding - (a form of covalent bonding) Allows electrons to "freely" move from one atom to another, usually good thermal and electrical conductors.

There are 14 ways in which atoms can "fit" together to fill all of space.  These are called lattice types.


What is a mineral?
For something to be classified as a mineral it must satisfy these criteria:

  1. It is an inorganic, naturally occurring element or compound in a solid state.  (It is disputed whether naturally occurring liquids at room temperature, e.g. water and mercury, should be considered a mineral.)
  2. It has a composition that is fixed or varies within narrow limits.
  3. It has a characteristic crystalline structure.

What is a rock?
A rock is just an assemblage of one or more minerals.  A typical rock may vary considerably in mineral composition.

Rocks are divided into 3 major groups

  • Igneous rocks are formed by the cooling of magma (below the surface) or lava (above the surface).  These rocks are the ancestors of all rocks.
  • Sedimentary rocks are made up of particles derived from the breakdown of pre-existing rocks.  Lithification is the process that changes unconsolidated deposits into rock.
  • Metamorphic rocks have changed their form due to exposure to pressure, heat, and/or chemically active fluids.

The Rock Cycle describes the relationship between these three categories of rocks.

Rock Cycle

Rock Cycle
The arrows indicate a change in the environment.

Rock Cycle - Related Web Links

GOOGLE search for Rock Cycle
Rock Cycle
from U. of Texas at El Paso, Rock Cycle from the University of Saskatchewan Dept. of Geological Sciences
Rock Cycle from the course Introduction to Petrology, University of British Columbia
Information Guide on rock collecting from the USGS
Google - Search for Rock Cycle

 

Minerals - Lecture Notes

There exists over 4,000 different minerals that have been classified.  Some of these minerals are much more abundant than others.

Just 10 elements make up 99% (by weight) of the Earth's crust.  These are O, Si, Al, Fe, Ca, Na, K, Mg, Ti, H.  Most (74.3%) of the minerals in the Earth's crust contain Oxygen (O) and Silicon (Si).  This is why the Silicate mineral family (minerals having the ion SiO4) compose 90% of all rock forming minerals.

Minerals can be identified by

  • Using X-ray diffraction (determines crystal structure) and mass spectrometry (determines composition)

or

  • examining the physical, macroscopic properties of the mineral.

Suppose you are excavating for a residential basement and find a very shiny and interesting rock.  Is it worth anything and what is it?  Your tool shed probably does not have an x-ray diffraction device or a mass spectrometer.  Thus, the physical properties that one can identify with the unaided eye and a few simple tools becomes useful.

Physical Properties of Minerals

Crystal Form (or Habit) is the external shape produced by a minerals internal crystalline structure.  This happens when a mineral grows (or solidifies) without interference or obstacle.  It will be bounded by planar surfaces symmetrically arranged.

Cleavage is the tendency of a mineral to break in certain preferred directions along smooth planes.

Twinning is the intergrowth of two or more single crystals of the same mineral with different geometric orientations.

Striations are parallel, threadlike lines or narrow bands running across crystal faces or cleavage surfaces.

Hardness is determined by the relative ease or difficulty with which one mineral can scratch another.  (A characteristic determined by the internal atomic arrangements and chemical bonding.)  Using known mineral samples to test the hardness of an unknown is common practice.

Mohs Hardness Scale
(This scale is not "linear".  Such that, a hardness of 2 might be twice as hard as 1, but 5 might be 10 times the hardness of 1 on Mohs scale.)

Specific Gravity is, essentially, the minerals density when compared to the density of water.

Specific Gravity

[Information that may be useful:  In the SI system of units (metric system), weight has units of Newtons (N) and mass has units of Kilograms (kg).  In the "Old English" system, weight has units of Pounds (lb) and mass is measured in Slugs (?).  Weight and mass are related by the equation W=mg, where W is the weight, m is the mass, and g is the acceleration due to gravity (g=9.8m/s2=32ft/s2 on the surface of the earth).  Of course, mass can also be measured in grams, but one should not use grams in the weight formula if you want the weight to be in Newtons.]

Streak is the color of a mineral in a finely powdered form.  This is usually determined by running the mineral across a piece of unglazed porcelain called a streak plate (or just unglazed white tile found at the hardware store).  Streak properties of minerals.

Luster is the appearance or "quality" of light reflected from a minerals surface.  It is often divided into metallic and non-metallic luster.

Color is a property that describes itself.  It is the color of a mineral.  Most geologist consider this property a weak differentiator among minerals.  But a few minerals will possess a very "striking" color.

Other Properties:
Magnetic (technically speaking it is usually ferromagnetism) - is it attracted to a permanent magnet?
Fluorescence - becomes luminescent during exposure to UV or IR light.
Phosphorescence - stays luminescent even after exposure to UV or IR light.
Pyroelectricity - temperature changes will cause charges to build up on the surface.
Piezoelectricity - pressure changes will cause charges to build up on the surface.
Solubility - does it effervesce in dilute HCl acid?  (Carbonate minerals usually do effervesce.)
Fusibility - can an intense heat (flame) cause two samples to fuse together? 
Fracture - minerals can break in distinctive ways that are different than cleavage.
Tenacity - resistance to breaking when exposed to mechanical stress.

In essence, any physical property that differs between minerals can be used to help identify minerals!

Mineral Groupings (or "Families")
(Web links provided by the theimage and Amethyst Galleries, Inc., )

Mineral Groupings

Some interesting minerals

    The clay mineral Montmorillonite (commonly referred to as the expansive or swelling clay) can expand up to 15 times its original volume depending on the subsurface moisture content.  It can also produce up to 500 kN/m2 of pressure when expanding.

    A large number of you probably have Quartz wrist watches.  Quartz has the property of being piezoelectric.  It vibrates with a very regular pattern when placed into an oscillating electric circuit.  The vibrations occur at a rate of 100,000 vibrations per second.  Some quartz clocks are accurate to within 1 second every 10 years.

Keeping the carrots straight: A carrot is a vegetable.  The term karat refers to the purity of gold.  A 24 karat necklace is pure gold but a 14 karat necklace is an alloy with copper or silver mixed with it.  And a carat is a measure of the mass of a precious gem (1 carat = 0.2 grams).

Minerals - Related Web Links

GOOGLE search for Minerals
The Athena Mineralogy gargantuan mineral database
A list of mineral properties from Amethyst Galleries, Inc.
A very large mineralogy database, contains physical and optical properties, pictures, several classification systems
The roving "geologist" on Mars (a.k.a. the Mars Pathfinder mission)
Description of mineral properties from UTEP
Description of ions and minerals and mineral properties from University of Saskatchewan
Google - Search for Mineral Properties

On-line Lecture Notes

GOOGLE search for mineral lecture notes
Minerals by Steve Dutch
, Natural and Applied Sciences, UW-Green Bay
Dr. Andy Frank's Physical Geology Minerals
Dr. Pamela Gore's Mineral lecture notes
Atoms, Elements, and Minerals - Dr. Steven D. Schafersman, Miami University
Dr. Susan DeBari's lecture notes on Minerals and Rocks
Google - Search for Lectures on Minerals

 

Raw Materials - Lecture Notes

Having a sufficient supply of raw materials is vital to the economy of a nation.  These raw materials must be "mined" from the earth or recycled (if possible).

Energy Resources
   Renewable resources can be replenished over a short time span (about 100 years maximum).               Examples include: hydroelectric, wind, tides, geothermal, solar, biomass

    Non-renewable resources cannot be replenished over a short time span (usually needs millions of years to replenish).  Once consumed it is gone forever!
            Examples include: fossil fuels (Oil, coal, natural gas, etc.), uranium

Energy costs are a big factor when estimating construction jobs.  The energy to process the materials (iron, wood, steel, etc.), the energy to transport the goods to the site, the energy to run the equipment (compactors, welders, vehicles, backhoes, etc.).  Heating energy is sometimes needed for sites during the winter.

Energy sources (percent of the total energy consumed that comes from that source): 40% petroleum, 23% natural gas, 22% coal, 8% nuclear, 5% hydroelectric, 2% others.

The big picture
(Source:  A. Hobson, Physics: Concepts and Connections, Prentice Hall 1995)

Percentage of the total U.S. resource consumed by 1992 Years remaining until total resource is gone at present annual rate
Coal 2 3600
Oil 70 25
Natural Gas 40 69
Uranium (without breeder reactors) 8 200

 

Is There a Looming Oil Crunch?

As reflected in the table above, the world supply of oil appears heading for a disaster.  To truly understand the situation one needs to know (1) how much oil has been extracted to date, (2) an estimate of known reserves and the amount that can be pumped from them before they dry up, and (3) an educated guess at the quantity of oil that remains yet to be discovered and exploited.  The first is easy to determine the last two are quite difficult for a variety of reasons - one of them being that companies have an incentive to make unrealistically large projections of known reserves.  The latest information about this situation comes from a Scientific American article in March 1998 with a special report titled Preventing the Next Oil Crunch:

"...(authors) conclude that before the next decade is over the flood of conventional oil will crest, and production will enter a permanent decline.  These analysts marshal an impressive body of statistics to support their projections.  If they are right, the world will need to move quickly to avoid the price hikes, recessions and political struggles that oil shortages - or the threats of them - have historically provoked."
Web page and group devoted to the study of when oil production will peak.

Mineral deposits are usually divided into metallic and nonmetallic.
    Metallic - Fe, Al, Chromium, Tin, Uranium, Silver, Mercury, Gold
    Nonmetallic - Salt, Building Stones (or Dimension Stones), Sand and Gravel, Phosphorus, Sulfur

If a mineral deposit is economically worthwhile to mine, then it is called an ore.  A high grade ore consists of a high concentration of a valuable mineral in a localized volume of earth.

Ways to extract the materials from the ground

Open-pit or "Strip" mining is carried out at the surface and digs down removing the overlaying material.
Underground mining involves tunneling into the earth and removing material.  Usually consists of mine shafts down to a horizontal layer of ore being removed.
Placer mining usually involves the separation of valuable metals or nonmetals from unconsolidated material near the surface.  Bauxite, the principle ore of aluminum, is often extracted this way.

Video of Soudan Underground Mine (~90 Mb, will require fast internet connection)

Mining --> Crushing --> Chemical processing to extract important element or compound

If you are hunting for a particular mineral for mining, it is important to know how the deposits are usually formed (this link talks about mineral exploration and production).  Igneous activity can produce high grade ores from fractionalization or magmatic segregation of magma chambers.  Iron oxides have been found to solidify and settle towards the bottom of the chamber during cooling.  Hydrothermal activity may carry metallic ions into surrounding rocks.  Many gold and silver deposits have precipitated from hydrothermal solutions.  Some iron rich rock layers have resulted from sedimentation of pre-cambrian seas.  An example is the taconite mines in the Lake Superior region.

Annual Nonmetallic Consumption by the U.S. (1996)

Annual Nonmetallic Consumption by the U.S. (1996)

Annual Metallic consumption by the U.S. (1996): 
    Iron and Steel - 1.5x1011 kg
    Aluminum - 6.6x109 kg
    Copper - 2.7x109 kg
    Lead - 1.6x109 kg
    Zinc - 1.3x109 kg

Strategic Mineral is one that is in short supply within a nations boundaries but is vital for the nations economy.  These minerals are usually stockpiled during peace time or mined from "conquested" lands.  Tin, chromium, manganese, and tungsten are considered strategic minerals in the U.S.  (Some would argue that wars have been fought over "strategic minerals", e.g. Persian Gulf war, if one considers oil to be such a mineral.)

(An article in the November '96 issue of Physics Today has a fascinating article on the Soviet Unions efforts to join the nuclear club immediately after WWII.  The article was titled Trinity at Dubna.)
Paragraphs from this article:

    "Materials for the witches cauldron....During World War II, uranium was in short supply.  There was no market for it.  In the Soviet Union in 1945 there were about five tonnes of uranium on hand and few known deposits or ore.  This lack of material formed the basis of the American belief that a Soviet A-bomb was decades away.
    Speakers at the Dubna conference revealed that a stash of 45 tonnes of uranium was located in eastern Germany at the end of the war.  Directed by good intelligence, that material was soon liberated.  Its delivery to Laboratory No. 2 allowed the Soviets to start work there on the F-1 reactor at once, saving perhaps a year's time.
    Simultaneously, a crash effort started to mine known Soviet uranium reserves, in some cases with horses.  Soon, 63,000 people were involved.  Major national radiological surveys began, with over 250 teams combing the entire USSR.  Every geologic survey, no matter what its original purpose, was to look for signs of radioactivity.  As a result the Soviet government found 50 uranium deposits with reserves of 84,000 tonnes.  In the decade of 1945-55, the Soviet uranium inventory grew from 5 tonnes to 6,800 tonnes."

Raw Materials - Related Web Links

Frequently Asked Questions on Nuclear Power
Wisconsin Electronic Reader (Image Gallery of Mining in Wisconsin)
Resources from the Dept. of Geology and Geophysics, UW-Madison (by Philip E. Brown)
Construction and Manufacturing
Mineral Law and Land Access
Energy Resources
Iron, Steel, Ferroalloy Metals
Nonferrous Metals
Case Study on Copper in the Lake Superior region
Chemical and Industrial Metals
Fertilizer and Chemicals
Environmental Geochemistry and Mining
Google - Search for Mineral Resources

Related businesses to Ceramics and Industrial Minerals
DECO Marble and Granite. LTD
A long list of U. S. Departments of Energy Efficiency and Renewable Energy Network.

On-line lecture notes

Mineral Resources - Dr. Steven D. Schafersman ,Miami University

Review Quizzes
Section 2

Review Quiz Section 2
Tarbuck and Lutgens, Essentials of Geology, Self-Quiz (Select Chapter Minerals)
Minerals
- Dr. Andy Frank's Review Exam
Minerals - North Dakota State University Self-Test, Geology 120