COBALT

COBALT. The word cobalt is commonly used to denote a metallic ore consisting of arsenic combined with the metal which is properly called cobalt. It therefore does not occur in a native state, but in that of different ores, which, according to their combinations, come under one or other of the following heads:

1. Gray cobalt, the octahedral cobalt pyrites of Mohs, and bright or tin-white cobalt of Phillips and Jameson, whose colour is white inclining to steel-gray, streak grayish black, and fracture uneven. It contains, according to Stromeyer,

It occurs both crystalline and massive, the crystals being generally rent and cracked. It is met with principally in veins accompanying ores of silver or copper, as at Freyberg, Annaberg, and particularly at Schneeberg in Saxony; at Joachimsthal in Bohemia; and at Wheel Sparrow, near Redruth, in Cornwall.

2. White cobalt. The hexahedral cobalt pyrites of Mohs, and the silver-white cobalt of Jameson. This generally occurs in cubes and pentagonal dodecahedrons, having a very bright metallic lustre, a silver-white colour tinged at times of a reddish hue, and a cleavage perfectly

Cobbing parallel to the faces of the cube. It contains, according to Stromeyer,

At Tunaberg in Sweden it is met with in large, resplendent, distinctly-pronounced crystals; also at Modum in Norway, and in Silesia. The richest known mines are, however, those of Wehna, in Sweden, where, though the ore only occurs massive, and is associated with mica slate, it is so easily obtained, and got in such considerable quantity, as to afford a source of much profit.

Both these ores give off a large quantity of arsenical fumes when exposed to the action of the blowpipe, and fuse only after being roasted. They impart a blue colour to borax and other fluxes, and afford a pink solution with nitric acid. The residuum of cobalt, after the sulphur, arsenic, and other volatile matters are driven off by calcination, is termed zaffre, and in that state it is imported into this country for the purpose of colouring earthenware and making smalt. The colouring power of oxide of cobalt on vitrifiable mixtures is greater perhaps than that of any other metal; one grain giving a full blue to 240 grains of glass.

The remaining ores of cobalt are the red cobalt, arsenate of cobalt, or cobalt bloom as it is called, possessing a beautiful crimson-red or peach-blossom colour, generally crystallized in small four-sided prisms, and for the most part a native of Schneeberg in Saxony, and Saalfeld in Thuringia; and cobalt-ochre, a black, brown, or even yellowish-coloured mineral, forming friable, indurated, earthy-like masses, which are generally soft to the touch, easily sectile, and of a comparatively low specific gravity.