Minerals and Mineral Identification



Introduction to Crystalline Solids (Minerals)

Properties of Minerals

Mineral Identification Tests

Mineral Classes


Introduction to Crystalline Solids (Minerals)

Easy to get excited about large mineral specimens

Can be quite showy (and expensive!)

Minerals usually come in smaller, less exciting sizes

Form the rocks on which we live

Form the basis of our civilization - both ancient and modern

Weapons, tools, comforts and adornments

DIGRESS TO: name something which is NOT dependent upon minerals

What is a mineral?

Solid - no liquids allowed!

Natural substance - not man-made

Inorganic - not coal

Chemical element or compound with definite ratios and formulas

FeS2 is always pyrite

Fixed internal structure

Graphite vs. diamond


Properties of Minerals

Chemical properties of minerals

What they are made of

Definite chemical formulas

Halite (ordinary table salt): NaCl

Composed of sodium (reactive solid) & chlorine (poisonous gas)

If it's not NaCl, it's not halite

Mafic vs. felsic

Fundamental differences in elemental composition lead to fundamental differences in the igneous rocks they form

This is VERY IMPORTANT so pay attention

Crystal structure

Easy to see in big specimens - much tougher when small, or not there

Some truly large minerals have been identified

Etta Mine - South Dakota

Spodumene "logs" over 10 feet long

Brazil: quartz crystals of several hundred pounds

Feldspar (forms 60% of earth's crust)

Norway: 7' X 12' X 30'

Ural Mtns.: A quarry was opened in a single crystal (30' X 30' X ?)

My experience in the Pala District

Stewart Lithia Dike: 40' long perthite crystal

White Queen: quartz crystal as roof support

Tourmaline Queen: my mining experience

External crystal form a reflection of the internal order

External form only evident if mineral was allowed to crystallize in open space

Euhedral: perfect crystal form

Subhedral: some external form

Anhedral: no visible crystal form

Six possible crystal systems are possible: See table 3-1, pg. 63

You will be required to recognize 2 of them:

Cubic system: halite, pyrite, flourite

Hexagonal system: quartz


Tests used in the identification of minerals

General Statements

Care of the specimins

Care of the equipment

Intro to magnification

Pass out ID sheet - review headings

Intro to Mineral ID Charts

Appendix pgs. 667-669

Based on luster, then hardness

Correct mistakes in book

The tests

Luster: Quantity and quality of light reflected from surface

Can be tough to use

Many minerals have a range of lusters

Color: Obvious but not always definitive

Sulfur is generally yellow, but most minerals can exhibit a range of possible colors

Streak: Can be definitive (ex. hematite) (Videodisc #403-407)

Hardness: See Table 2-2, pg. 30

Can vary due to impurities but usually definitive

Breakage pattern - VERY important!

Fracture: Uneven breakage

Special case: Conchoidal fracture (quartz)

Cleavage: The ability of a mineral to split along closely spaces parallel planes

(Videodisc #372-377)

Can have 1, 2, 3, 4, or 6 planes of cleavage

Can be obscured, but definitive when present

Perfect, Good in 2 directions, Poor, etc.

Specific Gravity:

"The weight of a specific volume of a mineral divided by the weight of an equal volume of water (at 4 deg. C.)"

Can vary due to impurities but usually definitive

Can be very important

Mafic vs. felsic

For example, variations in specific gravity allow miners to separate placer gold from the river gravel it is found in

The Fizz test (Videodisc #432)

Reaction to dilute HCl

Works for most minerals and rocks which contain calcium carbonate (CaCO3)

Calcite, limestone, dolomite, chalk, marble, etc.

Magnetism: Magnetite (Videodisc #419)

Taste: Halite, chalcanthite

Smell: Sulphur

Double refraction (Videodisc #418)

Pull out calcite samples

Black light (Videodisc #420-423)


Mineral classes

Usually based on primary supporting elements and/or compounds

Only 8 elements account for 98.5% of the crust

Fig. 3-4, page 66

Many mineral groups based on the common elements (no surprise here)

Silicates - Most common mineral class in crust (and probably mantle)

Most rock forming minerals are silicates

Discuss the SiO4 tetrahedron

Basic building block of the crust

Oxygen composes 46.6% of the crust by weight

And nearly 94% by volume!

The crust is essentially a boxwork of oxygen joined together by silica and a few other elements

Quartz & Feldspar - lots and lots

Feldspar composes 60% of the crust

Know the feldspars or die!

Non-silicate rock forming minerals


Calcite, Dolomite




Common ore minerals


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