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Native Elements and Sulfides
MineralogyNovember 9, 2012
Native elements
Native Metals
3 groups:
Gold Group
Platinum Group
Iron Group
Native Semimetals
Native Nonmetals
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
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
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
diamond
graphite
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
sphalerite
wurtzite
chalcopyrite
Pyrite