Rocks and Minerals I

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Rocks and Minerals I
http//www.geology.wisc.edu/maher/air/air14.htm
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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
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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/sedimenta
ry.html
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Minerals

• Lets take a look at some of the characteristics
  of minerals and their tests.

Lou Perloff
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Mineral Formulas

• A mineral has a definite chemical formula such
  as NaCl, called halite CuAl6(PO4)4(OH)84(H2O),
  known as turquoise or (K(Mg,Fe)3AlSi3O10)(OH)2)
  which is biotite.

John Betts
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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
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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
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Mineral Luster
Lusters metallic shiny dull
non-metallic adamantine earthy pearly silky g
reasy 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?id1091
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Mineral Hardness
Diamond hardest

• Hardness is a minerals 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
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Mineral Hardness
Hardness (Mohs) Mineral Absolute Hardness
1 Talc (Mg3Si4O10(OH)2) 1
2 Gypsum (CaSO42H2O) 3
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
9 Corundum (Al2O3) 400
10 Diamond (C) 1500
2.5 Fingernail
2.53 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
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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. DM/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
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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.h
tm
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
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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