Mineral Database

Mineral Database
Mineralogy of Wales

Troilite

Crystal System: Hexagonal
Formula: FeS
Status of Occurrence: Confirmed Occurrence
Distribution: Rare
Chemical Composition: Iron sulphide
Method(s) of Verification: Pontllyfni meteorite - EMPA (Graham et al., 1977)
Chemical Group:
  • Sulphides
Geological Context:
  • Igneous/metamorphic extraterrestrial
Introduction: troilite occurs chiefly in meteorites and has also been noted in rock samples from the Moon. Terrestrial occurences are limited to ultrabasic rocks, serpentinites and magmatic iron-nickel-copper sulphide deposits. Troilite is stoichiometric ('pure') iron sulphide, but unlike pyrrhotite (non-stoichiometric FeS) it is not magnetic.
Occurrence in Wales: the Welsh occurrence of troilite is related to one of very few meteorite falls actually recovered from Wales. The meteorite fell on April 14th, 1931 at 11:53am on Coch-y-Bug Farm, Pontllyfni, Gwynedd and a fragment of 5oz was recovered (King, 1932). For more data on this event, please visit the meteorites page (About Mineralogy section).
Key Localities:
  • Coch-y-Bug Farm, Pontllyfni, Gwynedd: troilite is abundant in the forsterite chondrite meteorite that fell at this place, occurring, along with daubreelite, as inclusions varying from <1 µm to 100 µm across. These are associated with (but not intergrown with) the iron-nickel metal alloys taenite and kamacite. The sulphides and metals make up 46 wt% of the meteorite, and are intergrown with olivine and orthopyroxene (Graham et al., 1977).
References:
  • Graham, A.L., Easton, A.J. & Hutchison, R., 1977 Forsterite chondrites; the meterorites Kakangari, Mount Morris (Wisconsin), Pontlyfni, and Winona.  Mineralogical Magazine, 41, 201-210.
  • King, A., 1932 The meteorite of 1931 April 14.  Journal of the British Astronomical Association, vol 42, 328-332.