Page 238 - A Practical Introduction to Optical Mineralogy

Mineral Formula - R % Colour - VHN Anisotropy Distinguished properties/resemblance See
range (associations) page
cubanite CuFe,S, 35 light grey isotropic intergrown with orthorhombic cubanite
cubic (pinkish) (Cu-Fe-S)
cuprite Cu,O 25-30 light grey 180-220 strong deep red internal reflections
(bluish) (Cu, Fe-OH, Cu-Fe- S, Ag)

digenite cu.s, 22 light grey 60-70 isotropic 142
(bluish) (Cu-Fe-S)
djurleite Cu ~. •• s ---> ---> ---> ---> resembles chalcocite

elect rum (Au,Ag) 83 light yellow 30-40 isotropic resembles gold 178
(Au-Te-Bi-Cu-Fe-As-Sb-Pb- S)
enargite Cu,AsS. 25-29 light grey 130-580 strong cleavage II (110)
(pinkish) colourful (Cu-Fe-Sb-As-S)
galena PbS 43 white 70-80 isotropic triangular cleavage pits 145
(Pb-Ag-Sb-As-S, sulphides)
gersdorffite (Ni,Co,Fe)AsS 47-54 white 520-910 isotropic zoning, cleavage II (100) gives
(pinkish) triangular pits
(Fe-Co--Ni-As-S)

glaucodot (Co,Fe)AsS 45-50 white 840-1280 distinct idiomorphic, cleavage; as inclusions
orthorhombic in cobaltite
(Co--Ni-As- S)
goethite HFeO, 17 grey 770- 820 distinct Colloform , botryoidal or elongate 170
orthorhombic crystals; red to brown internal
reflections
(in limonite, Fe-minerals, gossans)

gold Au 74 bright yellow 50 isotropic very bright; as inclusions in 178
sulphides; in fractures; soft
(Au-Te-Bi- Cu-Fe-As-Sb-Pb-S)

goldfieldite Cu,(Te,Sb )S. 32 light grey isotropic zoned
(Fe-Zn-S, Au-Ag-Te, Bi)
(brownish)
graphite c 6-16 dark grey 10 strong deformed flakes ; bireflectance strong; 178
(brownish) to cleavage
(graphitic schists, graphite ' veins')
grey

hematite Fe,O, 25-30 light grey 920- 1060 strong tabular crystals, microcrystalline 161
masses; lamellar twinning; weak
bireflectance
(Fe-Ti-0)

hydrocarbon < 5 dark grey isotropic rounded grains, interstitial masses,
frosted surface, low reflectance but
no internal reflections
(sedimentary rocks, barite, carbonate,
sulphide veins, U)

ilmenite FeTiO, 18-21 light grey 520-700 moderate occasional twinning; lamellar 162
(slightly inclusions of hematite
pinkish) (Fe-Ti-0)

iron Fe 65 bright white 120-290 isotropic rounded grains
(Fe- Ni-S, moon, meteorites)

jacobsite (Mn,Fe,Mg)(Fe,Mn),O. 19 grey (brownish 720-750 isotropic rounded grains; fine aggregates;
-greenish) strongly magnetic; resembles braunite
(Mn-minerals; Fe-OH; in metamorphic
rocks)