This document provides an introduction to minerals, including their definition, classification, and methods of identification. It defines minerals as solid, naturally occurring, inorganic substances with a definite chemical composition and crystalline structure. Minerals are classified based on their chemical composition, with major groups including silicates, oxides, sulfides, halides, carbonates, and sulfates. Identification of minerals involves tests of color, luster, hardness, streak, crystal shape, cleavage/fracture, and other properties. Proper identification requires using multiple tests as no single test is definitive and some minerals can look similar.
2. Introduction to Minerals
Outline
• Criteria to “qualify” as a mineral
– Formation of minerals (in brief)
• Classification of minerals
• Identification of minerals
3. Definition of a Mineral
• Five Criteria:
– Solid
– Naturally Occurring
– Inorganic
– Definite Chemical Composition
– Crystal (adj: Crystalline)
4. Definition of a Mineral
Naturally Occurring
http://en.wikipedia.org/wiki/File:Glass-Ball.jpg
5. Definition of a Mineral
Inorganic
http://en.wikipedia.org/wiki/File:Kandiszucker_wei%C3%9F.jpg
6. Definition of a Mineral
Definite Chemical Composition
• Example:
– “Halite” just is NaCl
• There may be slight
impurities.
http://en.wikipedia.org/wiki/File:Selpologne.jpg
7. Definition of a Mineral
Crystal Structure
• Atoms form an orderly
and repeating
arrangement
http://en.wikipedia.org/wiki/File:Halite-249324.jpg
8. Formation of Minerals
• Must have conditions for good crystal growth!
• One: Slow cooling of “magma” – hot, liquid
rock material
• Two: Slow evaporation of water that has
dissolved compounds
– Forms an “evaporite” (see next slide)
10. Classification of Minerals
• Classified based on CHEMICAL COMPOSITION
– i.e., what they’re made of
– there is tolerance or “fudge factor” for some small
impurities
– The following are MAJOR groups, but not
exhaustive!
12. Classification of Minerals
Oxides
• Oxides contain oxygen in the chemical formula
(except when part of another class)
• Example: Hematite, Fe2O3
http://en.wikipedia.org/wiki/File:Hematite.bear.660pix.jpg
13. Classification of Minerals
Sulfides
• Sulfides contain sulfur in the chemical formula
(except when part of another class)
• Example: Pyrite, FeS2
http://en.wikipedia.org/wiki/File:2780M-pyrite1.jpg
14. Classification of Minerals:
Halides
• Halides contain a halogen (Group 17 element)
in the chemical formula
• Example: Fluorite, CaF2
http://en.wikipedia.org/wiki/File:Fluorite_crystals_%28Cullen_Hall_of_Gems_and_Minerals%29.jpg
15. Classification of Minerals:
Carbonates
• Carbonates contain the polyatomic ion
“carbonate” in the chemical formula
– i.e., CO3 (which has a 2- charge)
• Example: Calcite, CaCO3
• Note that this is NOT an oxide.
http://en.wikipedia.org/wiki/File:Calcite_jaune.jpg
16. Classification of Minerals
Sulfates
• Sulfates contain the polyatomic ion “sulfate”
in the chemical formula
– i.e., SO4 (which has a 2- charge)
• Example: Celestite, SrSO4
• Note that this is NOT an oxide NOR a sulfide.
http://en.wikipedia.org/wiki/File:Celestitemadagascar.jpg
17. Identification of Minerals
• Guiding Principles
– A single test is never good enough.
– Many minerals STRONGLY RESEMBLE other ones.
– Even individual samples can be outside the norm.
19. ID of Minerals:
Luster
• Metallic
vs.
• Nonmetallic
– glassy, vitreous, dull, etc.
http://en.wikipedia.org/wiki/File:Citrin_cut.jpg
http://en.wikipedia.org/wiki/File:2780M-pyrite1.jpg
20. ID of Minerals:
Scratch Test (Hardness)
• Mohs Scale of Hardness
• “To scratch, or to be scratched?”
– System is just relative rankings (“ordinal”)
http://geology.csupomona.edu/mineral/mohs.gif
21. ID of Minerals:
Streak Test
http://en.wikipedia.org/wiki/File:Streak_plate_with_Pyrite_and_Rhodochrosite.jpg
22. ID of Minerals:
Crystal Shape
http://en.wikipedia.org/wiki/File:2780M-pyrite1.jpg
http://en.wikipedia.org/wiki/File:Halite-249324.jpg
23. ID of Minerals:
Breaking Good?
• CLEAVAGE
– Some minerals break along a flat plane, forming a
smooth surface
– E.g., “basal
cleavage” is
breaking into
thin sheets
http://en.wikipedia.org/wiki/File:Fluorita_green.jpeg
24. ID of Minerals:
Breaking Bad?!
• FRACTURE
– Other minerals break in jagged or curved ways
“conchoidal fracture” -
forms smooth, rounded edges
http://en.wikipedia.org/wiki/File:Green_quartz.jpg
http://en.wikipedia.org/wiki/File:Lipari-Obsidienne_%285%29.jpg
25. ID of Minerals:
Miscellaneous Tests
• Taste test?! (DO NOT DO THIS ONE.)
• Magnetism test
• UV light test (at bottom left)
• Optical test (for calcite only, at bottom right)
• Carbonate / acid test (see next slide)
http://en.wikipedia.org/wiki/File:FluoriteUV.jpg
http://en.wikipedia.org/wiki/File:Crystal_on_graph_paper.jpg
26. ID of Minerals:
Carbonate / Acid Test
• Any carbonate mineral should react with
hydrochloric acid:
XCO3 + 2HCl → XCl2 + H2O + CO2
27. Check Yourself
• Attempt to classify these minerals:
– Molybdenite, MoS2
– Kyanite, Al2SiO5
– Blodite, Na2Mg(SO4)2
• Why is color not a good indicator of a
mineral’s identity?
• What kinds of conditions form good mineral
samples?
