Page 241 - A Practical Introduction to Optical Mineralogy

Mineral Formula - R % Colour -VHN Anisotropy Distinguishing properties/resemblance See
range (associations) page

safftorite (Co,Fe,Ni)As, 55-66 white (bluish) 430-990 strong concentric radiating aggregates with
(zoned) other minerals; star shaped twins
(Co-Ni-Fe-As, Bi, U, Ag, sulphides)
scheelite cawo. 10 dark grey 290-460 distinct rhombohedral cleavages; abundant
white internal reflections
(wolframite, Cu-Fe-As-S, Bi-S,
Sn, Au)
schriebersite (Fe,Ni),P white weak elongate inclusions in iron minerals
(Fe-N i-S, meteorites, moon)
silver Ag 95 bright white 50-120 isotropic scratches easily; skeletal or dendritic 179
(metallic) (Co-Ni-Fe-As, oxidised sulphides)
skutterudite (Co,Ni,Fe)As,_x 53 white 270-970 isotropic cleavage traces, compositional zoning
variable (yellowish (weak (Co-N i-F-As-S, Au, Ag, U, Mo, Bi)
bluish or anisotropy)
pinkish)
sphalerite (Zn,Fe)S 17 grey 190-210 isotropic colourless to red internal reflections; 151
irregular fractures and cleavage pits
(sulphides)
spinel MgAl,O. 8 dark grey 860-1650 isotropic octahedral, rounded; internal 165
reflections; as inclusions in magnetite
(Fe-Ti-0)
stannite Cu,SnFeS. 28-29 light grey 140-330 strong cleavage, triangular pits, pleochroism,
(greenish to lamellar and cross-hatch twinning
brownish) (sulphides, Sn-W-As-Bi-Au)

stibnite Sb,S, 30--40 light grey 40-110 very strong acicular or bladed; distinct 153
to white bireflectance; cleavage traces;
(slightly deformation twinning
(Ag-Pb-Sb-S, Fe- S, Au, Hg-S)
brownish)
taenite (Fe,Ni) white isotropic lamellae in kamacite
(yellowish) (Fe-Ni-S, Fe-Ti-Cr-0, meteorites)

tennantite Cu 10 (Zn,Fe) 2 31 light grey 320-370 isotropic polycrystalline aggregates 154
(Cu-Fe-S, galena, sphalerite)
(As,Sb ).S 13
tetradymite Bi,Te,S 50-52 white 30-50 distinct hexagonal cross sections, basal
(yellowish) cleavage
(Au-Bi-Te-S, Cu-Fe-S)

tetrahedrite (Cu,Ag) , 0 (Zn,Fe,Hg), 31 light grey 320-370 isotropic polycrystalline aggregates 154
(Cu-Fe-S, galena, sphalerite)
(Sb,As ).S 13
titanomagnetite (Fe,Ti),O. 17 grey 720-730 isotropic homogeneous only if formed by rapid 163
(brownish or (weak cooling, otherwise intergrown with
pinkish) anisotropy) Fe-Ti-0 phases
(Fe-Ti-0 in igneous and metamorphic
rocks)

todorokite (H 2 0)< 2 Mn<,(O,OH) , 6 20 light grey - strong columnar to fibrous aggregates,
botryoidal; cleavage traces
(Mn-Fe-0; deep sea Mn nodules)

troilite FeS yellow strong resembles pyrrhotite; rare
(brownish) (colourful) (Fe-Ni-S, moon, meteorites)

ulvospinel Fe,TiO. 17 brownish isotropic as fine intergrowths in titaniferous 163
grey magnetite; octahedra
(Fe-Ti-Cr-0, igneous, moon)