Minerals

Dr. R. B. SchultzDr. 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 structureCrystal structure depends on sizes of and charges on ions Polymorphs -- same chemical composition, different crystal structures  Mafic silicate minerals Most common minerals are silicatesAll 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 silicatesFelsic silicates are silicate minerals that don't contain magnesium or iron, are light in color Examples: feldspar, quartz, clay minerals, muscovite mica  Silicate mineral structuresBasic 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 structureCations serve as links between tetrahedra; no sharing of oxygens e.g. olivine, and garnet, which also happen to be mafic silicates  Single chain silicatesAdjacent 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 silicatesTwo 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 silicatesEvery oxygen in each tetrahedron is shared to form 3-D framework e.g. feldspar, quartz, which are also non-mafic  Common non-silicate mineralsCalcite -- 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 PropertiesGeologists 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. CleavageRefers 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. HardnessRefers 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. ColorVaries in many minerals, e.g. quartz Some minerals come in just one color; other are many colors/many varieties 5. StreakRefers to color of mark left by rubbing mineral against a streak plate (unglazed porcelain) streak does not vary even if color does.  6. Other PropertiesSome minerals are magnetic Some minerals effervesce ("fizz") in dilute acid Specific gravity (like density) 

Moh's Hardness Scale (Commit this to memory) 

1.0            TALC2.0          GYPSUM2.5 FINGERNAIL3.0          CALCITE3.5          COPPER PENNY4.0          FLUORITE5.0          APATITE5.5          STEEL KNIFE BLADE/GLASS PLATE6.0          ORTHOCLASE FELDSPAR7.0          QUARTZ8.0          TOPAZ9.0          CORUNDUM (RUBY)10 DIAMOND

Crystal structureCrystal 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 Silica TetrahedronTetrahedron

Oxygens Silicon

Isolated tetrahedral structureCations serve as links between tetrahedra; no sharing of oxygens e.g. olivine, and garnet, which also happen to be mafic silicates  Single chain silicatesAdjacent 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 silicatesTwo 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 silicatesEvery 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 additiveCalcite -- 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

CleavageRefers 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

HardnessRefers 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

ColorVaries in many minerals, e.g. quartz VERY unreliable.Some minerals come in just one color; other are many colors/many varieties. StreakRefers to color of mark left by rubbing mineral against a

streak plate (unglazed porcelain). Streak does not vary even if color does.

 Other PropertiesSome minerals are magnetic (i.e., magnetite)Some minerals effervesce ("fizz") in dilute acid (calcite)Specific gravity (like density) galena has a high specific

gravity.

Mineral Chemical composition

Crystalline structure Ions

Cation Anion

Silicate Mafic

Felsic Silica tetrahedron

Single chain Double chain

Sheet silicate Framework silicate

Non-silicate Physical properties

Habit Luster

Streak Cleavage

Hardness Moh’s Hardness Scale

Key Terminology

Pertinent Web SitesAmateur 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 http://comp.uark.edu/~sboss/vrockbag.htm#minerals