Download Rocks and Minerals I

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/se
dimentary.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
Patrick Laird
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.
Mike Streeter
Patrick Laird
Floyd Hawk
Mineral Streak
Patrick Laird
http://geology.csupomona.edu/alert/mineral/streak.htm
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.
Mineral Luster
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
Lusters:
metallic
shiny
dull
non-metallic
adamantine
earthy
pearly
silky
greasy
resinous
glassy
http://webmineral.com/specimens/picshow.php?id=1091
Mineral Hardness
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.
Diamond
hardest
Lou Perloff
Talc
softest
www.yuprocks.com
Mineral Hardness
Hardness
(Mohs)
Mineral
Absolute
Hardness
2.5
Fingernail
1
Talc (Mg3Si4O10(OH)2)
1
2.5–3
Gold, Silver
2
Gypsum (CaSO4·2H2O)
3
3
Copper penny
3
Calcite (CaCO3)
9
4-4.5
Platinum
4
Fluorite (CaF2)
21
4-5
Iron
5
Apatite (Ca5(PO4)3(OH-,Cl-,F))
48
5.5
Knife blade
6
Orthoclase Feldspar
(KAlSi3O8)
72
6-7
Glass
7
Quartz (SiO2)
100
6.5
Iron pyrite
8
Topaz (Al2SiO4(OH-,F-)2)
200
9
Corundum (Al2O3)
400
7+
Hardened
steel file
10
Diamond (C)
1500
Density or Specific Gravity
All minerals have a
density. Densities
that are high or low
may be helpful in
identifying the
mineral.
Galena
very dense
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.
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