Minerals geology

Minerals

Dr. R. B. Schultz


The earth is made of rocks, which are in turn made of
minerals. In this part of the course we'll learn how
to identify common minerals and rocks.
In order for something to be classified as a mineral, it
must meet five (5) criterion:
Minerals are:
·        1. Naturally occurring,
·        2. Inorganic,
·        3. Have known chemical compositions
·        4. Have definite physical properties.
5. Are solid
·       
They are usually (although not always)
crystalline.


 Mineral Classification
Minerals are classified based on chemical composition and crystal structure.
Minerals are made of different ions bonded together.
Ions are charged atoms
•        Cations are positively charged whereas
•        Anions are negatively charged
 
Common ions in earth's crust:
O - most common ion (anion)
Si, Al, Fe, Ca, Na, K, Mg, (Cations)

Minerals are made mainly of these ions
 
 
 
Crystal structure
Crystal structure depends on sizes of and charges on ions
Polymorphs -- same chemical composition, different crystal structures
 
Mafic silicate minerals
Most common minerals are silicates
All silicate minerals contain silicon and oxygen
Silicates that also contains iron or magnesium are called mafic silicate minerals
 
Mafic silicate minerals are dark in color
Examples: of mafic silicates: olivine, pyroxene, amphibole, and biotite mica
 
Felsic silicates
Felsic silicates are silicate minerals that don't contain magnesium or iron, are light in color
Examples: feldspar, quartz, clay minerals, muscovite mica
 
Silicate mineral structures
Basic building block: silica tetrahedron
Silica tetrahedron is a silicon ion bonded to 4 oxygen ions
Silicon is positively charged (+4)
Oxygen is negatively charged (-2)
Net charge on tetrahedron: -4
Because tetrahedron is negatively charged, it is attracted to cations
Tetrahedra may link together by a cation (e.g. Mg, Fe, Na, Ca, K) serving as a bridge, or
Tetrahedra may link together by sharing oxygens
 

 
Isolated tetrahedral structure
Cations serve as links between tetrahedra; no sharing of oxygens
e.g. olivine, and garnet, which also happen to be mafic silicates
 
Single chain silicates
Adjacent tetrahedra form a chain by sharing 2 of their oxygens with neighboring tetrahedra
e.g. pyroxenes, which also happen to be mafic silicates
 
Double chain silicates
Two chains can link up by sharing oxygens
e.g. amphiboles, which are mafic silicates too
 
Sheet silicates
Sheets are formed when each tetrahedron shares 3 of its oxygens with its neighbors
e.g. micas, biotite (mafic) and muscovite (non-mafic), and clay minerals, which are non-mafic silicates
 
Framework silicates
Every oxygen in each tetrahedron is shared to form 3-D framework
e.g. feldspar, quartz, which are also non-mafic
 
Common non-silicate minerals
Calcite -- calcium carbonate -- Limestone is made of calcite.
Dolomite -- calcium magnesium carbonate
Gypsum -- calcium sulfate
Galena -- lead sulfide
Pyrite -- iron sulfide
Halite -- sodium chloride (table salt)
 
How to Identify Minerals: Physical Properties

Geologists determine the identity of an unknown mineral by describing its physical properties. They then use a reference book to find out what mineral has those properties. We will learn to describe the physical properties.
 
1. Habit refers to the overall shape of the mineral
use terms like: "equant" (3 dimensions of the mineral have about the same length, like a cube or sphere),
“elongate" (one direction is long but the other 2 are short, like a pencil), or "platy" (one dimension is short, other 2 are long like a sheet of paper)
isolated tetrahedra & framework silicate minerals tend to be equant in habit; chain silicates tend to be elongate, sheet silicates are platy
 
2. Cleavage
Refers to very smooth, flat, shiny breakage surfaces
These special breakage surfaces correspond to zones of weak bonding in the crystal structure
To describe cleavage, must determine the number of unique cleavage planes (directions) and their angle with respect to each other (e.g. salt breaks into cubes, with cleavage in 3 directions, all at 90 degrees)
 
3. Hardness
Refers to "scratchability" of the minerals harder minerals will scratch softer minerals
Rank minerals according to hardness using the Moh's scale
Fingernails are about 2.5 on Moh's scale; glass or steel knife is about 5.5; use these common items to estimate hardness of a mineral.
 
4. Color
Varies in many minerals, e.g. quartz
Some minerals come in just one color; other are many colors/many varieties
 
5. Streak
Refers to color of mark left by rubbing mineral against a streak plate (unglazed porcelain) streak does not vary even if color does.
 
6. Other Properties
Some minerals are magnetic
Some minerals effervesce ("fizz") in dilute acid
Specific gravity (like density )
 
Moh's Hardness Scale (Commit this to memory)

 
1.0            TALC
2.0          GYPSUM
2.5
FINGERNAIL
3.0          CALCITE
3.5          COPPER PENNY
4.0          FLUORITE
5.0          APATITE
5.5          STEEL KNIFE BLADE/GLASS PLATE
6.0          ORTHOCLASE FELDSPAR
7.0          QUARTZ
8.0          TOPAZ
9.0          CORUNDUM (RUBY)
10
DIAMOND


Crystal structure
Crystal structure depends on sizes of and charges on ions
 
Most common mineral group is the silicates
All silicate minerals contain silicon and oxygen
1. Mafic silicate minerals contain iron or magnesium and
are dark in color.
Examples: olivine, pyroxene, amphibole, and biotite
mica
2. Felsic silicates don't contain magnesium or iron, and
are light in color.
Examples: feldspar, quartz, clay minerals, muscovite

mica


Mafic silicate
Felsic silicate


Silicate mineral structures
Basic building block: silica tetrahedron
Silica tetrahedron is a silicon ion bonded to 4 oxygen ions
Silicon is positively charged (+4)
Oxygen is negatively charged (-2)
Net charge on tetrahedron: -4
Because entire tetrahedron is negatively charged, it is
attracted to cations
Tetrahedra may link together by a cation (e.g. Mg, Fe, Na,
Ca, K) serving as a bridge, or may link together by sharing
oxygens
 
 


Silica
Tetrahedron

Oxygens

Silicon

Isolated tetrahedral structure
Cations serve as links between tetrahedra; no sharing of oxygens
e.g. olivine, and garnet, which also happen to be mafic silicates
 
Single chain silicates
Adjacent tetrahedra form a chain by sharing 2 of their oxygens with
neighboring tetrahedra
e.g. pyroxenes, which also happen to be mafic silicates
 
Double chain silicates
Two chains can link up by sharing oxygens
e.g. amphiboles, which are mafic silicates too
 
Sheet silicates
Sheets are formed when each tetrahedron shares 3 of its oxygens with its
neighbors
e.g. micas, biotite (mafic) and muscovite (non-mafic), and clay minerals, which
are non-mafic silicates
 
Framework silicates
Every oxygen in each tetrahedron is shared to form 3-D framework
e.g. feldspar, quartz, which are also non-mafic
 




Common non-silicate minerals
Fluorite – used as a toothpaste additive
Calcite -- calcium carbonate -- Limestone is made of calcite.

Dolomite -- calcium magnesium carbonate
Gypsum -- calcium sulfate
Galena -- lead sulfide
Pyrite -- iron sulfide
Halite -- sodium chloride (table salt)



How to Identify Minerals: Physical Properties
Geologists determine the identity of an unknown mineral by describing its
physical properties. They then use a reference book to find out what
mineral has those properties. We will learn to describe the physical
properties.
 
1. Habit refers to the overall shape of the mineral. Scientists use terms
like: "equant" (3 dimensions of the mineral have about the same length,
like a cube or sphere), “elongate" (one direction is long but the other 2
are short, like a pencil), or "platy" (one dimension is short, other 2 are
long like a sheet of paper)
Isolated tetrahedra & framework silicate minerals tend to be equant in
habit; chain silicates tend to be elongate, sheet silicates are platy

 
2. Luster refers to the light reflected off of the mineral and its overall
quality. Minerals can be termed: glassy, opaque, transparent, shiny, or
most commonly: metallic and non-metallic.
One of the first determinations a geologist must make is whether the
mineral in metallic or non-metallic.

Non-metallic mineral

Metallic mineral


Cleavage
Refers to very smooth, flat, shiny breakage surfaces
These special breakage surfaces correspond to zones of
weak bonding in the crystal structure.
To describe cleavage, one must determine the number of
unique cleavage planes (directions) and their angle with
respect to each other (e.g. salt breaks into cubes,
with cleavage in 3 directions, all at 90 degrees)
NO
cleavage

 


Hardness

Refers to "scratchability" or resistance to being scratched. Harder
minerals will scratch softer minerals.
Geologists rank minerals according to hardness using the Moh's scale
Moh's Hardness Scale (Commit this to memory)
1.0     TALC
2.0    GYPSUM
2.5
FINGERNAIL
3.0    CALCITE

3.5    COPPER PENNY
4.0    FLUORITE (Note the spelling!)
5.0    APATITE
5.5    STEEL KNIFE BLADE/GLASS PLATE
6.0    ORTHOCLASE FELDSPAR
7.0    QUARTZ
8.0     TOPAZ
9.0     CORUNDUM (RUBY)
10.0 DIAMOND


Color
Varies in many minerals, e.g. quartz
VERY unreliable.
Some minerals come in just one color;
other are many colors/many varieties.
 
Streak
Refers to color of mark left by rubbing mineral against a streak
plate (unglazed porcelain). Streak does not vary even if color
does.
 
Other Properties
Some minerals are magnetic (i.e., magnetite)
Some minerals effervesce ("fizz") in dilute acid (calcite)
Specific gravity (like density) galena has a high specific gravity.


Key Terminology
Mineral

Crystalline structure
Cation
Silicate
Felsic
Single chain
Sheet silicate
Non-silicate
Habit
Streak
Hardness

Chemical composition
Ions
Anion
Mafic
Silica tetrahedron
Double chain
Framework silicate
Physical properties
Luster
Cleavage
Moh’s Hardness Scale


Pertinent Web Sites
Amateur Mineralogy Links
A very extensive listing of links to sites related to mineralogy.
Ask a Geologist
If you have questions, a professional geologist is here to help.
Ecole des Mines de Paris Mineralogy

Here are some beautiful mineral pictures from a museum in Paris.
Gems and Precious Stones
Jill Banfield's (University of Wisconsin-Madison) integrated body of information about gems and gemstones.
Gold Institute
A good commercial site with a lot of information about gold.
Gold Prospecting
A good source for information about recreational gold prospecting.
Mineral and Gemstone Kingdom
This site contains a comprehensive list of minerals and their properties.
Mineral and Rock Description (National Park Service)
Mineral and rock photographs and descriptions from the National Park Service.
Mineral Data Links
Links to several mineralogy related Web sites.
Mineral Descriptions and Images
The Mineral Gallery is a constantly growing collection of mineral descriptions, images, and specimens, together with several ways of accessing these descriptions.
Mineralogy and Petrology Research on the Web
An extensive list of mineralogy and petrology resources on the Web.
Mineralogy Database
This extensive mineral database contains more than 5,000 pages of mineral data. There are 3,874 individual mineral species data descriptions.
Mineralogy Links (University of Oxford)
An extensive listing of mineralogy and minerals related sites.
Mineral Identification Tutorial
Mineral identification tutorial from Texas A & M University.
Mineral Photographs
A comprehensive collection of mineral and gemstone photographs from The Image.
Mineral Resources Program (USGS)
The USGS Mineral Resources Program is responsible for providing and communicating current, unbiased information on the occurrence, quality, quantity, and availability of mineral
resources.
Minerals Links (Houghton Mifflin)
Links to several mineral sites, including class lecture notes, arranged by topic.

Minerals Links (NAGT)
An extensive listing of mineral links arranged by topic from the National Association of Geology Teachers (NAGT).
Minerals Links (University of Würzburg)
An extensive listing of mineral links including mineral descriptions and thin section images.
Minerals (Mineralogical Society of America)
The Mineralogical Society of America web site offers a good, general description of mineral properties, classification, etc. directed primarily
toward K-12 grade students.
Minerals (Trinity Mineral Company)
Beautiful photos of rare minerals offered for sale by the Trinity Mineral Company.
Minerals Information (USGS)
United States Geologic Survey (USGS) statistics and information on the worldwide supply, demand, and flow of minerals and materials essential
to the U.S. economy, the national security, and protection of the environment.
Minerals on the Internet
A wide variety of minerals-related sites sorted into relevant categories from Tasa Graphic Arts, Inc.
Mining and Mineral Resources
A great source for information about mining of mineral resources, mining news and trends, etc.
National Mining Association
The National Mining Association (NMA) represents the mining industry, mining equipment manufacturers, and other mining-related businesses,
throughout the United States.
Periodic Table of the Elements
In addition to listing a wealth of information about each element, this location also lists and describes numerous compounds.


Periodic Table of the Elements II
A great source for information on the elements.
Resource Fact Sheets (USGS)
United States Geological survey (USGS) activities in the natural resources theme area inventory the occurrence and assess the quantity and
quality of natural resources. Activities also include monitoring changes to natural resources, understanding the processes that form and affect

them, and forecasting the changes that may be expected in the future.
Resources from Space
University of Wisconsin course notes with links to several essays about resources from space.
Resource Sustainability
An essay that examines the future of Earth's resources.
Rock and Mineral Collecting (USGS)
Selected references on rocks, minerals, and gemstones from the United States Geological Survey (USGS).
Rockhounds Information Page
The Rockhounds Information Page offers many links to mineral and rock related Websites.
Smithsonian Gem & Mineral Collection
Images of mineral and gemstone specimens found in the Smithsonian Institution. (Not an official Smithsonian site)
Society for Mining, Metallurgy and Exploration, Inc.
The Society for Mining, Metallurgy, and Exploration (SME) is an international society of professionals in the minerals industry.
Society of Economic Geologists
The Society of Economic Geologists, Inc. (SEG) is an international organization of individual members with interests in the field of economic
geology.
State Minerals Information (USGS)
Statistics and information on the supply, demand, and flow of minerals and materials essential to the U.S. economy, the national security, and
protection of the environment from the United States Geological Survey (USGS).


Technical University of Clausthal
This site at a German university also shows some excellent mineral pictures.
Virtual Atlas of Opaque and Ore Minerals
This site provides over 400 full colour photomicrographs of the major ore-forming associations and opaque minerals in non-mineralized
rocks. It describes typical examples of each material from many classical localities throughout the world. For each association there is a
listing of the major (and important minor) primary ore minerals, alteration products and gangue, typical textures, a brief discussion of the
geology of the association and a list of references.
World Lecture Hall (University of Texas at Austin)
The World Lecture Hall features links to online courses in the United States and Canada.

Simplest to use for Mineral I.D. Lab:

Virtual Rock Bag

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