Introduction to Minerals Definition, Classification, Identification

Introduction to Minerals: Outline Criteria to “qualify” as a mineral Formation of minerals (in brief) Classification of minerals Identification of minerals

Definition of a Mineral Five Criteria: Solid Naturally Occurring Inorganic Definite Chemical Composition Crystal (adj: Crystalline)

Definition of a Mineral: Naturally Occurring If you’re paying attention, this is a NON-EXAMPLE. http://en.wikipedia.org/wiki/File:Glass-Ball.jpg

Definition of a Mineral: Inorganic If you’re paying attention, this is a NON-EXAMPLE. Sugar is the product of a living thing (i.e., “organic”) and is therefore not a mineral. http://en.wikipedia.org/wiki/File:Kandiszucker_wei%C3%9F.jpg

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

Definition of a Mineral: Crystal Structure Atoms form an orderly and repeating arrangement http://en.wikipedia.org/wiki/File:Halite-249324.jpg

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)

Formation of Minerals: Evaporite Example http://en.wikipedia.org/wiki/File:HaliteEncrustedCobbleDeadSea.JPG

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!

Classification of Minerals: Silicates Silicates contain silicon and oxygen in the chemical formula Example: Quartz, SiO2 (the simplest example) http://en.wikipedia.org/wiki/File:QuartzUSGOV.jpg

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

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

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

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

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

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.

ID of Minerals: Color Test http://en.wikipedia.org/wiki/File:Citrin_cut.jpg http://en.wikipedia.org/wiki/File:QuartzUSGOV.jpg http://en.wikipedia.org/wiki/File:Ele.rose.750pix.jpg http://en.wikipedia.org/wiki/File:Amethyst._Magaliesburg,_South_Africa.jpg http://en.wikipedia.org/wiki/File:Quarzo_morione.jpg http://en.wikipedia.org/wiki/File:Green_quartz.jpg

ID of Minerals: Luster Metallic vs. Nonmetallic glassy, vitreous, dull, etc. http://en.wikipedia.org/wiki/File:2780M-pyrite1.jpg http://en.wikipedia.org/wiki/File:Citrin_cut.jpg

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

ID of Minerals: Streak Test http://en.wikipedia.org/wiki/File:Streak_plate_with_Pyrite_and_Rhodochrosite.jpg

ID of Minerals: Crystal Shape http://en.wikipedia.org/wiki/File:2780M-pyrite1.jpg http://en.wikipedia.org/wiki/File:Halite-249324.jpg

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

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

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:Crystal_on_graph_paper.jpg http://en.wikipedia.org/wiki/File:FluoriteUV.jpg

ID of Minerals: Carbonate / Acid Test Any carbonate mineral should react with hydrochloric acid: XCO3 + 2HCl → XCl2 + H2O + CO2

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?

MINERALS