Sulfides Simple sulfides – based on close-packed sulfur atoms, with metals in void spaces. Complex sulfides – based on molecular like clusters, chains or sheets.

Simple Sulfides Sulfides with tetrahedral coordination Sulfides with octahedral coordination Sulfides with mixed octahedral and tetrahedral coordination Sulfides with unusual coordination

Sulfides with tetrahedral coordination

Sphalerite β-ZnS

Sphalerite (β-ZnS) has cubic close-packed sulfur atoms with Zn in half of the tetrahedral sites. Stacking direction is along the cube diagonal with ABC stacking sequence producing a face-centred cubic unit cell.

wurtzite α-ZnS

chalcopyrite

Chalcopyrite’s structure is tetragonal but consists essentially of two superimposed sphalerite cell, but differs because of the two different kinds of atoms, Cu and Fe.

Tetrahedrite Cu12Sb4S13

(a) sphalerite (b) chalcopyrite (c) tetrahedrite

Enargite Cu3AsS4

If an oblique lattice has a ≈ b and γ ≈ 120º , a nearly hexagonal primitive lattice becomes a centred one. A third perpendicular c direction yields a C-centred orthorhombic lattice.

Derivative Structures Cubic Close-packed Hexagonal Close-packed Lonsdaleite Diamond Wurtzite α-ZnS Sphalerite β-ZnS Enargite Cu3AsS4 Chalcopyrite CuFeS2 Tetrahedrite Cu12Sb4S13

The unit cell of sphalerite is analogous to that of diamond in that the sulfur atoms are CCP as the carbon atoms are in diamond. Zinc atoms fit in one-half of the tetrahedral spaces. The base of the tetragonal cell of chalcopyrite (a = 5.25Å) is very close to the cubic cell edge of sphalerite at (a =5.43Å). The c dimension at 10.32Å is approximately double the sphalerite cell edge. The unit cell of tetrahedrite is cubic and twice the size of that of sphalerite at a = 10.34Å. It is however a stuffed derivative in that there are more metals than sulfurs The unit cell of wurtzite is analogous to that of lonsdaleite in that the sulfur atoms are HCP as the carbon atoms are in lonsdaleite. Zinc atoms fit in one-half of the tetrahedral spaces. Enargite is orthorhombic, but its a-axis is equal to a√3 of wurtzite. The relationship here is one wherein any hexagonal Bravais lattice can be converted to an orthorhombic one.

bornite

bornite –tarnished “peacock ore”

Sulfides with octahedral coordination

pyrrhotite

galena Pyromorphite:Pb5(PO4)3Cl Galena

Sulfides with mixed octahedral and tetrahedral coordination

pentlandite (Ni,Fe)9S8

Sulfides with unusual coordination

Covellite CuS

Chalcocite Cu2S

Cinnabar Cinnabar Cinnabar HgS

acanthite, Ag2S pseudomorphous after argentite

molybdenite MoS2

Complex Sulfides Molecular-like clusters Molecular-like chains Molecular-like sheets

Pyrite pyrite

Pyrite pyrite

Cobaltite CoAsS

marcasite

(b) marcasite (a) pyrite

arsenopyrite

More Derivative Structures Pyrite group - cubic Marcasite group - orthorhombic Pyrite FeS2 Marcasite FeS2 - Cobaltite CoAsS Arsenopyrite FeAsS Cobaltite is orthorhombic, but has nearly equal axis lengths, hence close to cubic.

Skutterudite (Co,Ni)As3

CoAs3-x Skutterudite-type structures e.g. M4X12 filled skutterudite RM4X12 Typical compositions are (Co,Ni,Fe)As3-x so the end- members NiAs3-x and FeAs3-x nickel-skutterudite and ferro- skutterudite also exist R = La, Ce, Pr, Nd, Nd, Eu (i.e. rare earths M = Fe, Ru, Os X = P, As, Sb

orpiment realgar

Stibnite Stibnite Sb2S3

Stibnite Sb2S3 The structure is composed of chain-like groups of Sb (large circles) and S (small circles)

Yellow = S, Purple = Bi , Green = Pb, Blue = Cu bismuthinite krupkaite aikinite Bi2S3 CuPbBi3S6 CuPbBi S3 Yellow = S, Purple = Bi , Green = Pb, Blue = Cu The aikinite-bismuthinite (CuPbBiS3-Bi2S3) series of ordered derivatives (superstructures) is based on the incremental Bi + vacancy → Pb + Cu substitution (Petříček & Makovicky 2006). Members of the series include Aikinite, Bismuthinite, Emilite, Friedrichite, Gladite, Krupkaite, Paarite, Pekoite and Salzburgite.

Aikinite CuPbBiS3

Potosiite Pb6Sn2FeSb2S14