124 COPPER. hedron meet, an octahedron is formed,—a figure, however, which has been scarcely observed in the species. The crystals are small and seldom middle-sized;’usual- J leaped on one another, sometimes also superimposed. 1 heir surface is shining and splendent. Internally it is usually glistening; sometimes, however, it passes into shining, and has a metallic lustre. TI.e fracture is coarse and small-grained uneven; some times xt me ines to imperfect conchoidal, and such varieties have a blackish colour, the strongest lustre, and contain le greatest proportion of silver, and the least of copper. ie fragments arc indeterminate angular, and rather blunt-edged. It is more or less semi-hard. It gives a reddish-brown streak : some varieties do not produce any alteration of colour *. It is brittle. It is easily frangible. It is heavy. Specific gravity, 4.594, Wiedemann. 4.8648, llauv. 4.4460 to 4.560, Bournon. Chemical Characters. Before the blowpipe, it first decrepitates, and then melts into a greyish-coloured brittle metallic globule. During fusion it disengages a white arsenical vapour: to borax it communicates a yellowish colour inclining to red. Some varieties are difficult of fusion. Constituent * According to Count de Bournon, those varieties that afford a reddish- brown streak, may he presumed to contain a mixture of silver and antimony, generally combined together in the state of red silver-ore.