COB

( 304 ) COB

44 Cobalt55.5 Arfenic0.5 Sulphur

100.0

The latter procured from the fame ‘variety,36.66 Cobalt49. Arfenic5.66 Iron6.5 Sulphur

97.822.18 Lofs

100.

Similar differences are obfervable betweenthe analyfis of this variety by other chemifts, fothat it may be confidered as allowing of a con-fiderable range both in the proportion andnature of its conffituent parts, without mate-rially affedting its cryftallization. It appearshowever from Hauy, that when the cryftalsdifplay a lamellar fradture they contain anotable proportion of fulphur and iron. Kir-wan, Hauy and others, form two fpecies ofcobalt ore according to the preponderance ofarfenic or pyrites in their compofition. Bro-chant and the later German mineralogifts onthe other hand form three fpecies. This latterarrangement appears the moll ufeful and exadt,but as there are in reality no certain fpecificcharadters, we fhall confider the whole as onefpecies with three fubdivifions.

1. Sub-fpecies. White Cobalt. WeiJJer Speif-kobolt. Cobalt blanc. (Species 2d. of Kirw. andHauy.}’

The colour of this mineral when recentlybroken is tin-white, but its furface is generallyyellowifh, bluifh, reddifh, or greyifh, or iridef-eent like Heel that has been heated. It occursin mafs, diffeminated, kidney-fhaped, and rarelyin minute quadrangular tables, or imperfectcubes and octahedrons. Their external luftreis flight, but internally is brilliant and metallic.Its fracture is. fine-grained, uneven: whenbroken, it flies into fharp-edged irregular frag-ments. When in mafs it contains fine-grainedgranular diftindt concretions. It acquires apolifli by fridtion, is brittle and hard. Whenexpofed to the blow-pipe white cobalt meltswith great facility, giving out at the fame timea white vapour and ftrong arfenical odour, awhite brittle bead of metal remaining behind

which communicates a blue colour to glafs ofborax.

It is found in Norway , at Tunaberg inSweden, Annaberg in Saxony , alfo, thoughrarely, in Swabia and Stiria. In Saxony andNorway it is contained in beds of micaceousfchiftus accompanied by the red earthy cobalt,quartz, hornblende and pyrites.

2. Sub-fpecies. Dull-grey Cobalt. GrauerSpeijkobolt. Cobalt gtis (Sp. i. of Kirw. andHauy.)

The colour of this mineral is a clear fteelgrey, but by expofure to the air it acquires aniridefeent tarnifh. It occurs in mafs or diffe-minated, fometimes in kidney-fhaped or cluf-tered maffes, and very rarely in fpecular laminae.Its external luftre is very feeble, but internallyit exhibits a bright metallic luftre. Its fradtureis compadt, generally even, but fometimespaffing into flat conchoidal; its grain is remark-ably fine and clofe. Its fragments are fharp-edged, indeterminate. It is not fo hard as thepreceding, and is lefs brittle. Its fpecific gra-vity varies from 4.3 to 5.3 or even 5.5. Itgives a bluifh-grey metallic ftreak.

When expofed by itfelf to the blow-pipe itgives out an arfenical vapour and fmell, butfeldom fufes: when treated in the fame waywith borax it gives the flux a blue colour, andis reduced to a metallic globule.

A fpecimen of this from Cornwall was ana-lyzed by Klaproth , who procured from it about20 per cent, of cobalt, 24 of iron, and 33 ofarfenic, the remainder confifting partly of bif-muth and fulphur, together with earthy matter;fome varieties have alfo been found to containnickel and filver.

It is fomewhat rarer than the following fub-fpecies, but is found at Schneeberg , Freyberg,and other places in Saxony , at Joachimfthal inBohemia, Wittichen in Swabia , and Schmoel-nitz in Hungary ; alfo in Stiria, at Allemont inFrance, in Norway, and in Cornwall . It is ge-nerally accompanied by other cobaltic ores, bykupfernikel, native bifmuth, and filver.

3. Sub-fpecies. Bright white Cobalt. G/anzKobolt . Cobalt eclatant (Sp. 2. of Kirw. andHauy.)

The colour of this mineral is tin-white, buttarnifhes to greyifh, yellowifh, or iridefeent. Itis found in mafs, or diffeminated or inverting ;or of particular fhapes as cluftered, reniform,globular, interlaced, in fpangles ; or cryftallizedin cubes or octahedrons. The cryftals are ofmiddling fize or fmall, their furface is com-