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Lecture 3 - Mineralogy http://www.soest.hawaii.edu/coasts/gg101/index.html
Atoms build Earth’s Crust Molecules build Rocks build Minerals build
What is a Mineral? A mineral is a naturally occurring, inorganicsolid with an orderly internal arrangement of atoms (called crystalline structure) and a definite, but sometimes variable, chemical composition Page: 28[FCS1]Source? Page: 28[FCS2]According to Gloss of Geol, “used in mfr of glass, enamel, HF acid; steel not mentioned. ???
Hawaii’s most common mineral – volcanic Olivine Hawaii’s second most common mineral – marine Calcite
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
Chlorine = 7 electrons in outer shell Sodium = 1 electron in outer shell NaCl 7 e- in outer shell 1 e- in outer shell Ionic Bonding
H20 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)4- Single chain (SiO3)2- Double chain (Si4O11)6- Silicate sheet (Si2O5)2- Three-dimensional framework Chains of silicates form because Oxygen bonds with Silicon a second time (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
Must result in a neutral compound Silicon tetrahedrons form chains (SiO3)2- One cation may push another out of the latticework Single substitution Fe Mg Substitution Metallic cations fit inside the chains aluminum (Al3+) iron (Fe2+ or Fe3+) magnesium (Mg2+) calcium (Ca2+) potassium (K1+) sodium (Na1+) Na Ca Double substitution Si Al
Charge Size (nm) 46% oxygen (O2-) 0.132 2.3% potassium (K1+) 0.133 6% iron (Fe2+ or Fe3+) 0.064 4% magnesium (Mg2+) 0.066 28% silicon (Si4+) 0.042 8% aluminum (Al3+) 0.050 2.4% calcium (Ca2+) 0.099 2.1% sodium (Na1+) 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 Ca Substitution 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….