19 0 COPPER. j. When two elongated tetrahedral prisms are joined together by one of the sides of the prism, a twin- crystal is formed, which may be viewed as a te trahedral prism of 60° and 120°. When two opposite and lateral edges of this figure are deep ly truncated, the prism becomes six-sided. The lustre is intermediate between vitreous and resi nous. The fracture is foliated in the direction of the planes o the three-sided prism, but is uneven in every other di rection. It is transparent or semi-transparent. It scratches calcareous-spar with difficulty, but does not affect fluor-spar or heavy-spar. Specific gravity, 4.280. Chemical Characters. _ Before the blowpipe, it flows like water, and in cool ing crystallises in small rhomboidal plates of a brown c»- lour. ' Constituent Parts. Oxide of Copper, _ 54 Arsenic Acid, . . 30 Water, _ . . in 1() 0 99.12 Cheneoix, in Bliil. Klaproth, Beit. b. iii. Trans for 1801. s . 192. Geognostic and Geographic Situations. It occurs in the Cornish mines along with the other subspecies. 50.62 45.00 3.50 Third