Rocks and Minerals I http://www.geology.wisc.edu/~maher/air/air14.htm

What distinguishes rocks from minerals? Composition A mineral is homogeneous and has a fixed composition. It is formed through natural processes and is usually inorganic. It has a defined crystal structure. John Veevaert John H. Betts

What distinguishes rocks from minerals? Composition A rock is heterogeneous and formed from two or more minerals. Andrew Alden http://www2.vscc.cc.tn.us/svinson/geo100/sedimentary.html

Minerals Let’s take a look at some of the characteristics of minerals and their tests. Lou Perloff

Mineral Formulas A mineral has a definite chemical formula such as: NaCl, called halite; CuAl6(PO4)4(OH)8·4(H2O), known as turquoise; or (K(Mg,Fe)3AlSi3O10)(OH)2) which is biotite. John Betts

Mineral Color Color alone is not the best identifier of a mineral because even small inclusions may change the color you see. These photos are varied forms of quartz. Patrick Laird Mike Streeter Patrick Laird Floyd Hawk

Mineral Streak The powdered color of a mineral is characteristic. You can see the color by dragging the mineral across a rough surface. The result is called a streak. Patrick Laird http://geology.csupomona.edu/alert/mineral/streak.htm

Mineral Luster Lusters: metallic shiny dull non-metallic adamantine earthy pearly silky greasy resinous glassy Mineral luster is a term for describing the way light is reflected from the surface of a mineral. Galena - metallic http://webmineral.com/data/Galena.shtml Spodumene – glassy http://webmineral.com/specimens/picshow.php?id=1091

Mineral Hardness Diamond hardest Hardness is a mineral’s resistance to being scratched. A harder mineral will scratch a softer one. Hardness is a relative measure and is assigned a number based on the Mohs Scale. Lou Perloff Talc softest www.yuprocks.com

Mineral Hardness Hardness (Mohs) Mineral Absolute Hardness 1 Talc (Mg3Si4O10(OH)2) 2 Gypsum (CaSO4·2H2O) 3 Calcite (CaCO3) 9 4 Fluorite (CaF2) 21 5 Apatite (Ca5(PO4)3(OH-,Cl-,F-)) 48 6 Orthoclase Feldspar (KAlSi3O8) 72 7 Quartz (SiO2) 100 8 Topaz (Al2SiO4(OH-,F-)2) 200 Corundum (Al2O3) 400 10 Diamond (C) 1500 2.5 Fingernail 2.5–3 Gold, Silver 3 Copper penny 4-4.5 Platinum 4-5 Iron 5.5 Knife blade 6-7 Glass 6.5 Iron pyrite 7+ Hardened steel file

Density or Specific Gravity All minerals have a density. Densities that are high or low may be helpful in identifying the mineral. Density is the amount of matter in a given volume of the substance. D=M/V Specific gravity is the density of a substance compared to the density of water. Because specific gravity is a ratio with no units, it is often used in the place of density. Galena very dense Gypsum low density http://www.spaceman.ca/mineral/index.php?ViewImage=110

Other Mineral Properties Some carbonate minerals react to an acid such as HCl. The reaction produces carbon dioxide gas which will “fizz” on the mineral surface. http://geology.csupomona.edu/alert/mineral/other.htm Some minerals show magnetism or are attracted to magnets. Magnetite is the best example and has been used to make magnets. http://www.yourgemologist.com/magnetite.html

Identifying a Mineral When geologists or gemologists identify a mineral they use several properties. The properties they select depend on the sample itself and what they suspect the substance is. http://www.minerals.si.edu/images/gallery/mineral.htm