Transcript What is a Mineral? - Department of Geology

Good Web Sites about
Minerals:
• http://galaxy.einet.net/images/ge
ms/gems-icons.html
• Smithsonian Gem and Mineral
Collection -- lots of spectacular
mineral pictures and good
information
The Rock
Cycle
A model that
describes all the
crustal processes
by which rock is
formed,
modified,
transported,
decomposed,
and reformed.
N.Lindsley-Griffin, 1999
Rocks are made up of minerals
N. Lindsley-Griffin, 1999
What is a Mineral?
• Occurs naturally
• Not previously living
(inorganic)
• Solid
• Definite chemical
composition
• Orderly internal
atomic arrangement
N. Lindsley-Griffin, 1998
Ivory, bone, seashells, coral, petrified wood,
and other previously living things…
are NOT minerals
N. Lindsley-Griffin, 1998
Minerals
are made
up of
atoms
Atomic number =
number of protons;
gives atoms their
distinctive
characteristics.
Atomic mass =
protons plus neutrons
N. Lindsley-Griffin, 2000
Ions combine to form compounds
Here, the Li atom loses an electron to become a +
positively charged cation. The F atom gains an
electron to become a negatively charged anion.
Positive and negative charges attract each other to
form an IONIC BOND
N. Lindsley-Griffin, 1999
Covalent Bonding -- atoms share electrons
to form a strong bond.
Diamond
Diamond and graphite are the same
chemical composition (Carbon) but
exhibit very different internal structures.
Graphite
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Van der Waals Bonding -- a weak bond
caused by a weak secondary attraction
between molecules.
Graphite
N. Lindsley-Griffin, 1999
Orderly array of atoms in the mineral
Galena:
large atoms - sulfur, small - lead
As seen with a scanning-tunneling microscope
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The orderly arrangement of atoms in
Galena controls its physical properties.
Error in textbook on
Figure 2.7: Sulfur
atoms, not “oxygen”
Sulfur atom
N. Lindsley-Griffin, 1999
Crystal Interfacial Angles
Interfacial angles of a given mineral are constant
for all crystals
The faces of quartz always form 120-degree angles
© Houghton Mifflin 1998; Lindsley 2000
Crystal Interfacial Angles
• Even when the crystals are different sizes, angles
between equivalent faces are the same
• For different minerals, angles are different.
3
2
4
4
3
1
2
Quartz
N. Lindsley-Griffin, 1999
1
Habit
Habit - distinctive shape of the way the mineral
commonly (habitually) appears
N.Lindsley-Griffin, 1999
Concentric shells -- malachite
Habit
N. Lindsley-Griffin, 1998
Crystal shape and Habit result from
internal atomic structure
N. Lindsley-Griffin, 1998
Cleavage - tendency to break along
planes of weak bonds
N.Lindsley-Griffin, 1998
Mica cleaves along planes
of the weakest bonds
N. Lindsley-Griffin, 1998
Fracture describes how a mineral
breaks on an irregular surface rather
than along cleavage planes
Types of fracture:
Smooth
Rough
Splintery
Conchoidal
N. Lindsley-Griffin, 1998
Hardness
Hardness -- the resistance to being scratched
Mohs scale measures relative hardness,
the ability of one mineral to scratch another
Diamond
Corundum
Topaz
Quartz
Feldspar
Apatite
Fluorite
Calcite
Gypsum
Talc
10
9
8
7
6
5
4
3
2
1
Steel file
Glass
(6.5)
(5.5- 6)
Copper penny
Fingernail
(3.0)
(2.5)
Mohs hardness scale: 1 = softest mineral; 10 = hardest
© Houghton Mifflin 1998; Lindsley 2000
The 10 minerals of
Mohs relative hardness scale
3 Calcite
1 Talc
4 Fluorite
2 Gypsum
9 Corundum
6 Feldspar
N. Lindsley-Griffin, 1999
5 Apatite
7 Quartz
8 Topaz
10
Diamond
Luster
Luster - the appearance of a mineral
in reflected light
Types of luster:
Metallic
Nonmetallic
Pearly
Vitreous
Resinous
Silky
Dull
Earthy
Metallic luster of
pyrite
© Houghton Mifflin; N. Lindsley-Griffin, 1998.
Earthy luster of
limonite
Metallic Luster is characteristic of ore minerals
and others that contain metal cations.
N. Lindsley-Griffin, 1998
Resinous luster
in sphalerite
Pearly luster
in talc
N. Lindsley-Griffin, 1999
Color is useful in recognizing some
minerals, but not all
N. Lindsley-Griffin, 1998
Color adds value to gems
N. Lindsley-Griffin, 1999
Streak, the color of the mineral’s powder,
may be more useful than color in
identifying a mineral
N. Lindsley-Griffin, 1998
Structure of
Silicate Minerals
Most rocks consist of
silicate minerals.
The silicon-oxygen tetrahedron
is the building block of
silicate minerals
Four oxygen ions surround
a much smaller silicon ion
© Houghton Mifflin 1998; Lindsley, 2000
The silicate tetrahedron consists of 4 large
oxygen atoms around a smaller silicon atom
Expanded View
N. Lindsley-Griffin, 1999
Two tetrahedrons link
together by sharing an
oxygen at one corner
Silicate tetrahedrons can form chains,
sheets, and three-dimensional nets by
sharing their oxygen atoms. Each
influences mineral properties.
N. Lindsley-Grifin, 1999
Tetrahedral
Linkages
A. Isolated tetrahedra
- Olivine
B. Single chain
- Pyroxene
C. Double chain
- Amphibole
D. Sheets
- Micas, clay, talc
E. Framework
- Quartz, feldspar
© Houghton Mifflin 1998. All rights reserved
Polymorphs are minerals with the
same chemical composition, but
different internal atomic structures
N. Lindsley-Griffin, 1998
SUMMARY:
PHYSICAL PROPERTIES of MINERALS
Crystal Structure
Crystal Form
Interfacial Angles
Habit
Cleavage
Fracture
© Houghton Mifflin 1998; N. Lindsley-Griffin, 1999. All rights reserved
Hardness
Luster
Color
Streak
Specific Gravity
(Density)