258 Molybdena. Its colour is lead or fteel grey, with a lus tre. It has a lamellar texture, and is compofed of thin lamella;, placed over one another; the lamella are curved, flexible, and ftain paper with a luftre, more than plumbago. It is generally .found compadt, and feldom in particles. Its fpccific gravity is generally — 4,700. It can be cut with a knife, is fatty to the touch, can be volatilifed by a ftrong heat, and emits fulphujeous vapours. It is found likewife of regular lhape, as in lix fided plates, and in fix fidtd prifms, termi nating in fix fided pyramids, by double trun cation ; fuch a fpecimen Mr. Rafpe pofleffed, which I faw. Its matrix is feldfpar, lithom- arge, and quarzous rock. , It is found in Iceland—Sweden—Spain—at Altenberg in Saxony—at Schneeberg and Sch- lackenwald—in France—at Kolynan in Siberia, It is alfo found in rocks containing wolfram and tin ores. The^terra auftralis feems to be mixed with tnolybdena. GENUS