“This mineral occurs in small crystals embedded in prehnite, at Bishoptown, in Renfrewshire. It had been long supposed to be a variety of zinc-blende; but was first distinguished from that mineral by Lord Greenock. Two small crystals of it, sent to the author for chemical examination by Professor Jameson, appeared to be six-sided pyramids, and had a wine-yellow colour, conchoidal fracture, splendent and vitreous lustre, hardness about that of calcareous spar, orange-red streak, and considerable transparency.