Chapter 5

Section 1

What is a mineral?

Objectives1.Define mineral.

2. Compare the two main groups of minerals.

3. Identify the six types of silicate crystalline structure.

4. Describe three common nonsilicate crystalline structures.

How do you determine if a substance is a mineral?

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Classifying Minerals

Four basic questions:

Is the substance inorganic?

• Magnetite is inorganic and contains iron and oxygen.

• Coal is organic and is made from plants.

Is it naturally occurring?

• The mineral quartz occurs naturally in the earth.

• Steel and brass are man-made.

Is it a solid in crystalline form?

• Diamond has a solid crystalline structure.

• Petroleum and natural gas are naturally occurring but are not solids.

Does it have a definite chemical composition?

• The mineral fluorite is made of calcium and fluorine (CaF2)

• Concrete is made up of several substances.

Minerals:

• must be inorganic• must be naturally occurring• must be a solid with an internal crystalline

structure• must have a definite chemical makeup.

There are over 3,000 known minerals

• Many may be easily identified, although lab tests are needed to be conclusive.

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Elements in the Earth’s Crust

http://www.windows.ucar.edu/tour/link=/earth/geology/crust_elements.html&edu=high

Even though there are 92 elements that are naturally found, only eight of them are common in the rocks that

make up the Earth’s outer layer, the crust. Together, these 8 elements make up more than 98% of the crust.

• The 8 most common elements in Earth’s crust (by mass): 46.6% Oxygen (O)27.7% Silica (Si)8.1% Aluminum (Al)5.0% Iron (Fe)3.6% Calcium (Ca)2.8% Sodium (Na)2.6% Potassium (K)2.1% Magnesium (Mg)

• The picture on the left shows where these elements are located within the periodic table. Together, the elements oxygen and silicon make up most of the Earth’s crust including silicate minerals such as quartz and feldspar.

Identifying Minerals

Section 5.2

Objectives• Describe seven physical

properties that help distinguish one mineral from another.

• List 5 special properties that may help identify certain minerals

Physical properties of mineralsare a result of the chemical composition and

crystalline structure

Talc is highly variable, yet Sulfur is almost always yellowish.

• Talc

SulfurSulfur

ColorColor: Can be very characteristic for a few minerals, but is not important for others

Talc

Luster: the way light is reflectedeither Metallic or Non-metallic

Non-metallics are further described as:

dull(earthy) waxy

pearly (translucent)

glassy(transparent)

Hematite has a very

red streak

Streak:Streak: the color of the color of the powdered mineralthe powdered mineral

Cleavage and Fracturehow a mineral splits or how a mineral breaks

Moh’s Hardness Scale

Microsoft TableMicrosoft Table

We use a scale from 1 to 10 called MOH’S SCALE OF HARDNESS.

• Talc is a 1 and diamond is a 10.

• Most minerals fall between 3-6. The field scale can be very helpful:

Field Scale of Hardness

• Finger Nail 2.5

PennyPenny 3.5 3.5

Nail or Knife 5.0 to 5.5Nail or Knife 5.0 to 5.5

GlassGlass 5.5 to 6.0 5.5 to 6.0

Specific Gravity (heft):

Density = Mass/Volume

SG = Density of Sub./Density of H2O

Dry weight of Mineral SG = ----------------------------------- Dry weight - weight in water

Example low and high Specific Gravity

• Graphite (low)

Galena (high)Galena (high)

Unique Characteristics of a few minerals

Magnetism:

• Some minerals are attracted to a magnet.

Magnetite

Fluorescence:• Minerals which will glow under

an ultraviolet (black) light.

Minerals that continue to glow after the ultraviolet light is cut off are called phosphorescent.

Opal

Chatoyancy and Asterism

• Chatoyancy: Silky appearance due to large numbers of parallel mineral fibers.

• Asterism: Six-sided star shape when the mineral reflects light.

Radioactivity:

• Some radioactive minerals will emit charged particles that are detected by a geiger counter.

Uranitite

Malleability:

• Some minerals are bendable

Some minerals Some minerals are brittleare brittle

GarnetCopper

Feel:

• Some minerals feel greasy or soapy (unctuous)

Graphite

Solubility:

• Some minerals are soluble (will dissolve) in water

Halite

Double Refraction:

• Optical properties reveal a double image

Iceland Spar (Calcite)

Taste:

• Some minerals taste salty.

Halite

React with acids:

• Carbonates react with hydrochloric acid and give off CO2 gas

Calcite

Rocks: • are solid materials that

are made up of one or more minerals.

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Rock-forming minerals

• Of the 3,000 minerals, fewer than 20 form most of the earth’s crust.

Of these 20, only 10 are common, and these make up 90%

of the earth’s crust

All minerals can be classified into two main groups based on

their chemical composition.

• Silicates • Nonsilicates

Silicate minerals contain atoms of silicon (Si) and oxygen (O)

SiO2

Silicate minerals make up 96% of the earth’s crust.

Quartz

Feldspar(orthoclase)

Feldspar(plagioclase)

Silicates which are rich in iron and magnesium include:

Hornblende Olivine

Muscovite Biotite

Nonsilicate Minerals• Make up only 4% of the earth’s crust

• Six Major Groups

Carbonates

• Compounds that contain a carbonate group (CO3)

Halides

• Compounds that consist of chlorine or fluorine combined with sodium, potassium or calcium

Native Elements

• Elements uncombined with other elements

Oxides

• Compounds that contain oxygen and an element other than silicon

Hematite Fe2O3

Sulfates

• Compounds that contain a sulfate group (SO4)

Sulfides

• Compounds that consist of one or more elements combined with sulfur

Crystalline Structure

• a natural solid with a definite shape

The conditions under which minerals are produced do not usually allow large single crystals to grow.

Crystalline Structure of Silicate Minerals

• Silicon-oxygen tetrahedron

Silicon atom bonded to four atoms of oxygen in a pyramid arrangement

Variations

Ionic Silicates

• Silicon-oxygen tetrahedra linked only by atoms of elements other than silicon and oxygen

Single and Double Chained Silicates

Single Chain Silicates

• In single-chain silicates each tetrahedron is bonded to two others by shared oxygen atoms

• Minerals made up of single chains are called pyroxenes

Double Chain Silicates

• In double-chain silicates, two single chains of tetrahedra bond to each other.

• Minerals made up of double chains are called amphiboles

Tetrahedral Sheets

• Each tetrahedron shares three oxygen atoms with other tetrahedra.

• The fourth oxygen atom bonds with an atom of K or Al, which joins one sheet to another.

Examples of Tetrahedral Sheets

• Muscovite

• Biotite

Network Silicates

• Each tetrahedron is bonded to four neighboring tetrahedra

• Network silicates tend to form very hard crystals.

Examples of Network Silicates

• Quartz

• Feldspar

Assignments

• Section 5.1 Outline• Key Terms

• Direct Reading