Page 240 - A Practical Introduction to Optical Mineralogy

Mineral Formula - R % Colour - VHN Anisotropy Distinguishing properties/resemblance See
range (associations) page
orpiment As,S, 25 light grey 20-50 strong radiating aggregates; abundant
strong white to yellow internal
reflections
(realgar)
pentlandite (Fe,Ni).s, 44 white 200-230 isotropic triangular cleavage pits; alteration 148
(slightly along octahedral parting; as lamellae
yellowish) in pyrrhotite
(Cu-Ni-Fe-S)
perovskite (Ca,Na,A)(Ti,Nb)O, 15 grey 920-1130 very weak cubic octahedral habit; lamellar
A = rare earths twinning; strong white to brown
internal reflections
(Cu-Fe-Ti-0, alkaline igneous rocks)

pitchblende UO,_, 16 grey 670-800 isotropic radioactive; botryoidal masses, 166
variation in R; shrinkage cracks
(Ni-C<r-Ag-Bi, Au, sulphides)

platinum Pt 70 bright white 120--130 isotropic zoning; exsolved, intergrown phases
(yellowish) (incomplete of Pt group elements
extinction) (Pt-lr-Os-Rh-Ru-Pd, Fe-Cr-0,
Cu-Fe-S)

proustite Ag,AsS, 25-28 light grey 110-140 strong distinct bireflectance; red internal 148
(bluish) reflections
(Ag-Pb-Sb-As-S)

pseudobrookite Fe,TiO, 15 grey distinct red yellow internal reflections;
resembles rutile
(Fe-Ti-0)

psilomelane (Ba,Mn,Al,Fe,Si), 15--->30 grey-> light 200-810 strong fine crystalline aggregates, botryoidal;
grey (bluish) resembles cryptomelane
Mn,0 16 .(0,0H) 6
(Mn-0, Fe-OH; a weathering
product)
pyrargyrite Ag,SbS, 28-31 light grey 50-130 strong distinct bireflectance; red internal 148
(bluish) reflections
(Ag-Pb-Sb-As-S)

pyrite FeS, 54 white 1030-1240 isotropic idiomorphic, fractured; framboids 149
cubic (yellowish) (weak (common sulphide in all rock types)
anisotropy)

pyrolusite MnO, 30--36 light grey 80-1500 very strong coarse to cryptocrystalline; cleavage,
(yellowish) if well twinning
crystallised (Fe-Mn-0-0H; a weathering
product; veins)

pyrrhotite Fel _,s 40 white 230-320 strong polycrystalline aggregates, twinning; 150
(brownish or (colourful) alters readily; magnetic
(Cu-Fe-Ni-S, Fe-Ti-0)
pinkish)
rammelsbergite (Ni,Co,Fe)As, 60 bright white 460-830 strong radiating zoned aggregates, skeletal ;
(colourful) common lamellar twinning
(C<r-Ni-Fe-As, Ag, Ag-Sb-S)

realgar AsS 20--21 light grey 50-60 strong abundant strong yellow to red internal
reflections; interstitial
(orpiment, Fe-As-Sb-S, Fe-OH)

rutile TiO, 20--23 light grey 1070-1210 strong abundant bright internal reflections; 164
high temp. polymorph (bluish) twinning; acicular
(Fe-Ti-0, Fe-S)