Including...
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
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
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
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.
"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
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)
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
Carbonates
Calcite, Dolomite
Sulfates
Gypsum
Sulfides
Common ore minerals
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