COPPER. 26 



)o 



oblique four-sided prisms. The crystals are translucent, the mas- 

 sive varieties only translucent on the edges or opaque. It is 

 brittle, and yields to the knife. Its specific gravity is 3*66. Before 

 the blow-pipe it decrepitates, and becomes black. Its constituents 

 are, copper 58, carbonic acid 18, oxygen 12*5, water 11 5. Kla- 

 proth. It occurs principally in veins, with other ores of copper in 

 various parts of the world. 



. Compact Malachite. Pl. XXXVI. fig, 2, occurs most frequently 

 in mamillated or reniform concretions, botryoidal, tuberose, sta- 

 lactitic, cellular, and amorphous. Its colour is emerald and verdi- 

 gris °reen, and the lustre is shining and silky. It is opaque, rather 

 brittle, and easily frangible. Compact malachite bears a fine polish, 

 and is sometimes used as a green pigment. 



Sp. 9. Arsemate of Copper. Pl. XXXVI. fig. 3. — Strahlen- 

 kupfer, Karslen; Cuivre Arseniate, Hamj. — Copper combined 

 with arsenic presents several sub-species or varieties, differing greatly 

 in form and colour. The arseniate of copper may, however, be 

 readily distinguished from the carbonates by the following chemical 

 characters : " When pulverised," says Mr. Bakewell, " it imme- 

 diately communicates a blue colour to ammonia ; it decrepitates 

 on charcoal before the blow -pipe, emitting arsenical vapours, and 

 the parts in contact with the charcoal, are reduced to the metallic 

 state ; and it dissolves without effervescence in nitric acid." All 

 the varieties are found in the copper-mines of Cornwall. 



Octahedral Arseniate Diprismatic, Qlivemte, or Lenticular 

 Copper. — Linsenerz, IVerner ; Cuivre arseniate primitif, Hauy. — 

 Its usual colour is sky-blue ; it occurs sometimes apple or grass- 

 green, crystalized in obtuse octahedrons, nearly lenticular. It is 

 semi-transparent or translucent ; the lustre is vitreous ; it is brit- 

 tle ; the fracture is uneven $ and it yields to the knife. The spe- 

 cific gravity is 2-88. It contains peroxide of copper 49, arsenic 

 acid 14, water 35. Chenevix. 



Hexahedral Arseniate .—Cuivre arseniate lamelliforme, Hauy, 

 Copper mica, Jameson. — This variety is generally of a pure eme- 

 rald green colour, with considerable lustre and transparency. It 

 occurs massive, and in thin hexagonal tables, with a distinct 

 lamellar structure parallel to the hexagonal planes. It is softer 



