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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 1 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+) 2 Structure of the Atom Isotopes of an atom have variable number of neutrons (mass number) 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 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+) 3 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 4 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 5 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 6