native elements and sulfides mineralogy november 9, 2012
TRANSCRIPT
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Native Elements and Sulfides
MineralogyNovember 9, 2012
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Native elements
Native Metals
3 groups:
Gold Group
Platinum Group
Iron Group
Native Semimetals
Native Nonmetals
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Native Metals
Gold group
weak metallic bonds
all belong to same group in the periodic table (Ib, the transition metals.
isostructural
FCC lattice: 12-fold coordination
bonds intermediate between covalent and metallic; stronger and more directional bonds, leading to lower symmetry
Au and Ag: same ionic radius (1.44 A): complete SS
Cu (1.28 A)---limited SS with Au and Ag
Occurrence
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Platinum Group
harder, higher melting points
Pt and Ir: CCP
Iron Group
isometric, includes pure Fe (very rare—why?)
Ni-Fe metals: kamacite and taenite
Fe: 1.23 A, Ni: 1.24 A
kamacite: BCC 5.5 wt% Ni; taenite: FCC 27-65 wt% Ni
Fe-Ni phase diagram
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Native Semimetals
arsenic, antimony, bismuth
structures can’t be represented as simple packing of spheres—why
bond types intermediate between
Native Nonmetals
sulfur, diamond, graphite
Sulfur: orthorhombic, stable at atm p below 95.5 deg C; above that, monoclinic, melts above 119 C. 128 atoms in unit cell. Rings of 8 atoms form molecules. Rings bonded with…
Diamond: covalent; insulator; not close packed; sheets of C parallel to {111}; synthetic diamonds: who and when; lonsdalite; kimberlites
Graphite: conductor; 6-membered rings, each C with 3 nearest neighbors; 3 of 4 valence electrons in each C are locked in tight covalent bonds; the fourth wanders; organic mtl in mm rx
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diamond
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graphite
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Sulfides and Sulfosalts
Sulfides: most ore minerals, generally opaque, many have IV or VI coord; all types of bonds
Some important ones:
Sphalerite (low T) and wurtzite (high T) : both: Zn in IV coord, in sphalerite, Zn are in a FCC lattice; in wurtzite, HCP
Chalcopyrite: structure can be derived from the sphalerite structure: sub Cu and Fe for Zn
Pyrite: cubic; derivative of NaCl structure: replace Cl with 2S
Occurrence
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sphalerite
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wurtzite
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chalcopyrite
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Pyrite