Download Earth`s Crust

Lecture 3 - Mineralogy
Atoms build
Molecules build
http://www.soest.hawaii.edu/coasts/gg101/index.html
Rocks build
Minerals build
Earth’s
Crust
Common minerals that we mine and use.
Mineral Name
What It Is
Challcopyrite
Copper-iron-sulfur mineral; CuFeS2
Uses
Mined for copper
Feldspar
Large mineral family; aluminum-silicon-oxygen
composition; decomposes to form clays;
x(Al,Si)3O8, where x = various elements like
sodium, iron
Ceramics and porcelain
Fluorite
Calcium-fluorine mineral; CaF2
Mined for fluorine (its most important ore); steel
manufacturing
Galena
Lead and sulfur mineral; PbS, the leading ore
for lead
Mined for lead
Graphite
Pure carbon; C,
Pencil “lead” (replacing the actual lead metal
once used in pencils); dry lubricant
Gypsum
Hydrous-calcium-sulfur mineral; CaSO4 –
2H2O
Drywall, plaster of Paris
Halite
Sodium-Chloride; NaCl
Table salt, road salt, sodium, chlorine
Hematite
Iron-oxygen mineral; Fe2O3
Mined for iron
Magnetite
Iron-magnesium-oxygen mineral;
(Fe,Mg)Fe2O4
Mined for iron
Pyrite
Iron-sulfur mineral; FeS2
Mined for sulfur and iron
Quartz
Silicon-oxygen mineral; SiO2
In pure form, for making glass
Sphalerite
Zinc-iron-sulfur mineral; (Zn,Fe)S
Mined for zinc
Talc
Magnesium-silicon-oxygen-hydrogen mineral;
Mg3Si4O10(OH)2
Used in ceramics, paint, talcum powder,
plastics and lubricants
Calcite
Calcium carbonate CaCo3
Toothpaste, cement, drywall
Bingham Copper Mine – copper, silver, gold, molybdenum
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Hawaii’s most common mineral – volcanic Olivine
What is a Mineral?
A mineral is a naturally
occurring, inorganic solid
with an orderly internal
arrangement of atoms
(called crystalline structure)
and a definite, but sometimes
variable, chemical composition
Hawaii’s second most common
mineral – marine Calcite
Review the
structure of
an atom
How are minerals built?
Eight Abundant Elements in Crust
oxygen
46%
(O2-)
silicon
28%
(Si4+)
aluminum
8%
(Al3+)
iron
6%
(Fe2+ or Fe3+)
magnesium
4%
(Mg2+)
calcium
2.4%
(Ca2+)
potassium
2.3%
(K1+)
sodium
2.1%
(Na1+)
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Structure of the Atom Isotopes of an atom have variable
number of neutrons (mass number)
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If we drew a hydrogen atom to scale, making the nucleus
the diameter of a pencil, the electron would orbit about
0.5 km from the nucleus. The whole atom would be the size
of a baseball stadium…with so much empty space, how can
our world feel
f so solid?
i ?
Octet Rule…filled outer orbital
Atomic Number…number of protons
Mass Number…number of protons and neutrons
Most atoms exist in a charged
g
state due to the need to have
a filled outer shell - Ions
How are minerals built?
Octet Rule
Eight Abundant Elements in Crust
oxygen
46%
(O2-)
silicon
28%
(Si4+)
aluminum
8%
(Al3+)
iron
6%
(Fe2+ or Fe3+)
magnesium
4%
(Mg2+)
calcium
2.4%
(Ca2+)
potassium
2.3%
(K1+)
sodium
2.1%
(Na1+)
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Chlorine = 7 electrons in outer shell
Sodium = 1 electron in outer shell
NaCl
H2 0
7 e- in outer shell
P l molecule
Polar
l l
Oxygen = 6 electrons in outer shell
Hydrogen = 1 electron in outer shell
1 e- in outer
shell
Covalent Bonding
Ionic Bonding
46% oxygen (O2-)
28% silicon (Si4+)
8% aluminum (Al3+)
6% iron (Fe2+ or Fe3+)
4% magnesium (Mg2+)
2.4% calcium (Ca2+)
2 3% potassium
2.3%
t i
(K1+)
2.1% sodium (Na1+)
Crystallization
Slow cooling allows fewer (larger)
crystals = coarse texture to rock
Rapid cooling leads to many small
crystals = smooth texture to rock
These elements
Th
l
in
i a magma
chamber bond and form
minerals as the magma loses heat
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Most abundant elements? – silicon and oxygen
Silicon has 4 electrons in outer shell
= needs 4 more.
Oxygen has 6 electrons in outer shell
= needs 2 more.
(SiO4)4-
Oxygen still needs 1 more electron each
Single tetrahedron
(SiO4)4Single chain
(SiO3)2Double chain
(Si4O11)6-
Silicate sheet
((Si2O5)2-
Silica tetrahedrons will form
minerals with crystalline structure
consisting of unlinked tetrahedra,
chains, double chains, and sheets.
Silicon tetrahedrons form chains (SiO3)2-
Metallic cations fit inside the chains
aluminum (Al3+)
iron (Fe2+ or Fe3+)
magnesium (Mg2+)
calcium (Ca2+)
potassium (K1+)
(
)
sodium (Na1+)
Three-dimensional
Chains of silicates
framework (Si3O8)4form because Oxygen bonds
with Silicon a second time
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Silicon tetrahedrons form chains (SiO3)2Cations move into spaces in
silicate structures, but
they will only form compounds
that have no charge – neutral
(positive charges must
equal negative charges)
Single substitution
Fe
Must result in a
neutral compound
One cation may
push another out of the
latticework
Mg
Substitution
Metallic cations fit inside the chains
Na
Pairs of cations that
substitute for each
other
C
Ca
Double substitution
Si
aluminum (Al3+)
iron (Fe2+ or Fe3+)
magnesium (Mg2+)
calcium (Ca2+)
potassium (K1+)
sodium (Na1+)
Al
Charge
Size (nm)
46% oxygen (O2-)
2.3% potassium (K1+)
0.132
0.133
6% iron (Fe2+ or Fe3+)
4% magnesium (Mg2+)
28% silicon (Si4+)
8% aluminum (Al3+)
2.4% calcium (Ca2+)
2.1% sodium (Na1+)
0.064
0.066
0.042
0 050
0.050
0.099
0.097
Atoms in
a pair push
each other
outt off
position
As the Si and O build crystalline
structures and the metallic cations
play single and double
substitution, the entire magma
chamber grows into a solid mass
of minerals….
minerals
Cation Substitution: Mineral must be neutral
Na/Ca, Al/Si and Fe/Mg
Olivine: single tetrahedron (SiO4)4[Fe22+(SiO4)4-] or [Mg22+(SiO4)4-]
+4 +4 –8=0 or +4 +4 –8=0
Single
Substitution
Fe
Mg
Feldspar: 3-D framework (Si3O8)4[Na1+Al3+Si34+O82-]or [Ca2+Al23+Si24+O82-]
+1 +3 +12 –16=0 or +2 +6 +8 –16=0
Double
Na
Substitution Al
Ca
Si
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