Native Elements and Sulfides

1. Native Elements and Sulfides Mineralogy November 9, 2012

2. Native elements Native Metals 3 groups: Gold Group Platinum Group Iron Group Native Semimetals Native Nonmetals

3. 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

4. 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

6. 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

7. diamond

8. graphite

9. 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

10. sphalerite

11. wurtzite

12. chalcopyrite

13. Pyrite