Download How are minerals built?

Lecture 3 - Mineralogy
http://www.soest.hawaii.edu/coasts/gg101/index.html
Atoms build
Molecules build
Rocks build
Minerals build
Earth’s
Crust
Common minerals that we mine and use.
Mineral Name
What It Is
Uses
Challcopyrite
Copper-iron-sulfur mineral; CuFeS2
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
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 most common mineral – volcanic Olivine
Hawaii’s second most common
mineral – marine Calcite
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+)
Review the
structure of
an atom
Structure of the Atom 8
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 so solid?
Octet Rule…filled outer orbital
Atomic Number…number of protons
Mass Number…number of protons and neutrons
Isotopes of an atom have variable
number of neutrons (mass number)
Most atoms exist in a charged
state due to the need to have
a filled outer shell - Ions
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+)
Octet Rule
Chlorine = 7 electrons in outer shell
Sodium = 1 electron in outer shell
7 e- in outer shell
1 e- in outer
shell
Ionic Bonding
NaCl
H 20
Polar molecule
Oxygen = 6 electrons in outer shell
Hydrogen = 1 electron in outer shell
Covalent 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 (K1+)
2.1% sodium (Na1+)
These elements in a magma
chamber bond and form
minerals as the magma loses heat
Crystallization
Slow cooling allows fewer (larger)
crystals = coarse texture to rock
Rapid cooling leads to many small
crystals = smooth texture to rock
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
Silica tetrahedrons will form
minerals with crystalline structure
consisting of unlinked tetrahedra,
chains, double chains, and sheets.
Single tetrahedron
(SiO4)4Single chain
(SiO3)2Double chain
(Si4O11)6-
Silicate sheet
(Si2O5)2-
Chains of silicates
form because Oxygen bonds
with Silicon a second time
Three-dimensional
framework (Si3O8)4-
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+)
Cations move into spaces in
silicate structures, but
they will only form compounds
that have no charge – neutral
(positive charges must
equal negative charges)
Pairs of cations that
substitute for each
other
Silicon tetrahedrons form chains (SiO3)2-
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
Ca
Double substitution
Si
Al
aluminum (Al3+)
iron (Fe2+ or Fe3+)
magnesium (Mg2+)
calcium (Ca2+)
potassium (K1+)
sodium (Na1+)
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
0.099
0.097
Atoms in
a pair push
each other
out of
position
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
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….