PYRRHOTITE  , a

mineral species consisting of iron sulphide and crystallizing in the hexagonal system . The formula is Fen, Sn.+, where n may vary from 5 to 16; usually it is Fez Sa or Fell S,2, the latter being also the composition of the artificially prepared compound . Small amounts of nickel and cobalt are often present . Crystals have the form of hexagonal plates bounded at their edges by faces cf a hexagonal prism and pyramids, which are deeply striated horizontally . More frequently, however, the mineral is massive, with a laminar or granular structure . The colour is bronze-yellow and the lustre metallic; the streak is greyish-black . The hardness is 4 and the specific gravity 4 58–4.64 . The mineral is magnetic, sometimes with polarity, and it is therefore often called " magnetic pyrites." Pyrrhotite occurs in metalliferous veins, and as grains and plates disseminated through various rocks . In the gabbros and norites of Norway and Sweden it has been concentrated by magmatic differentiation at the margins of the igneous masses . Large bodies of massive pyrrhotite occur at Bodenmais in Bavaria and in Wheal Jane near Truro in Cornwall . Crystallized specimens are from the metalliferous veins at Morro Velho in Brazil, Kongsberg in Norway, and Andreasberg in the Harz . Crystals of pyrrhotite have also been observed in meteoric stones; but iron sulphide appears more commonly in meteorites, especially in meteoric irons, as troilite (FeS), which, if really distinct from pyrrhotite, has not been met with in terrestrial rocks .

(L . J .