TRIHEDRAL OLIVEN-ORE, 189 Gcognostic and Geographic Situations. It has been hitherto found only in the copper-mines of Cornwall. Second Subspecies. Trihedral Oliven-Orc. Nadelfdrmiges Oliven-Kupfer, Ilausmann. Arseniate of Copper, in the form of a trihedral prism, Bournon, Phil. Trans. 1801.—Cuivre arseniate trihedre, Brong. t. it. p_ gg Dichtes Olivenerz, Karsten, Tabel. s. 64.—Cuivre arseniate prismatiquo triangulaire, Hauy, Tabl. p. !)1.— Cuivre arseniate en prisme triedre, Bournon, Catalogue Mi- neralogique, p. 257 — Nadclformiges Olivenkupfer, Haus. b. iii. s. 1046.—Trihedral Arseniate, Atkin, p. 33. External Characters. Its colour is deep celandine-green ; but owing to its ready oxidation, it lias generally a blackish superficial tarnish. It occurs massive ; and crystallised in the following fi- »• * gures : 1. Three-sided prism, which is sometimes truncated on one of the edges: when the truncations be come deep, there is formed a 2. Four-sided prism, which is flat when two opposite planes become very broad. 3. Acute rhomboid, sometimes truncated on the dia gonally opposite angles. 4. Irregular octahedron. S. When