Lecture 3 - Mineralogy

http://www.soest.hawaii.edu/coasts/gg101/index.html

Atoms build

Molecules build

Minerals build

Rocks buildEarth’sCrust

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

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+)

How are minerals built?

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 canour world feel so solid?

Octet Rule…filled outer orbitalAtomic Number…number of protonsMass 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

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+)

How are minerals built?

Octet Rule

Chlorine = 7 electrons in outer shellSodium = 1 electron in outer shell

NaCl

Ionic Bonding

7 e- in outer shell

1 e- in outer shell

Covalent Bonding

Oxygen = 6 electrons in outer shellHydrogen = 1 electron in outer shell

H20

Polar molecule

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 magmachamber bond and form minerals as the magma loses heat

Slow cooling allows fewer (larger)crystals = coarse texture to rock

Rapid cooling leads to many small crystals = smooth texture to rock

Crystallization

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.

Oxygen still needs 1 more electron each

(SiO4)4-

Silica tetrahedrons will form minerals with crystalline structure consisting of unlinked tetrahedra, chains, double chains, and sheets.

Chains of silicatesform because Oxygen bonds with Silicon a second time

Single tetrahedron

Single chain

Double chain

Silicate sheet

(SiO4)4-

(SiO3)2-

(Si4O11)6-

(Si2O5)2-

Three-dimensionalframework (Si3O8)4-

Silicon tetrahedrons form chains

Metallic cations fit inside the chains

(SiO3)2-

aluminum (Al3+)iron (Fe2+ or Fe3+) magnesium (Mg2+)calcium (Ca2+)potassium (K1+)sodium (Na1+)

Pairs of cations thatsubstitute for eachother

Cations move into spaces in silicate structures, butthey will only form compounds that have no charge – neutral(positive charges must equal negative charges)

Silicon tetrahedrons form chains

Metallic cations fit inside the chains

(SiO3)2-

aluminum (Al3+)iron (Fe2+ or Fe3+) magnesium (Mg2+)calcium (Ca2+)potassium (K1+)sodium (Na1+)

One cation maypush another out of the latticework

SubstitutionMg

Fe

CaNa

Single substitution

Double substitution

Si

Al

Must result in aneutral compound

Charge Size (nm)46% oxygen (O2-) 0.1322.3% potassium (K1+) 0.133

6% iron (Fe2+ or Fe3+) 0.0644% magnesium (Mg2+) 0.066

28% silicon (Si4+) 0.0428% aluminum (Al3+) 0.050

2.4% calcium (Ca2+) 0.0992.1% sodium (Na1+) 0.097

Cation Substitution: Mineral must be neutral

Na/Ca, Al/Si and Fe/Mg

Olivine: single tetrahedron (SiO4)4-

[Fe22+(SiO4)4-] or [Mg2

2+(SiO4)4-] +4 +4 –8=0 or +4 +4 –8=0

Atoms ina pair pusheach otherout ofposition

Feldspar: 3-D framework (Si3O8)4-

[Na1+Al3+Si34+O8

2-]or [Ca2+Al23+Si2

4+O82-]

+1 +3 +12 –16=0 or +2 +6 +8 –16=0

SingleSubstitutionFe Mg

Double Na CaSubstitution Al 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….