COB

( 30 5 ) COB

jnonly fmooth. and brilliant, and marked withftriae on the fides of the primitive cube.

lhe frafture of the cryftals is lamellar, thatof the other varieties is line-grained uneven, orradiated. "When in mafs it prefents granular,or tedaceous, or lamellar diffindt concretions.In hardnefs it is fomewhat inferior to the pre-ceding fub-fpecies; when pulverized it is of afteel-grey colour. Sp. gr. 6.2 to 6.3. It is brittleand eafily broken.

When expofed to the blow-pipe it burnswith a faint white flame, difengaging arfenicalvapours; it then becomes black, is attractableby the magnet, and is with the utmod difficultyreduced to a metallic globule. It often affordsas much as 50 per cent, of reguline cobalt.

This is the commoneft of all the ores ofcobalt: it occurs for the moll part in primitivemountains, together with the other fpecies ofcobalt ore, with vitreous, red, and native filver,with arfenical and cupreous pyrites, &c. It ismet with in many parts of Germany , but efpe-cially in Saxony and Bohemia , at Tunaberg inSweden, at Modun in Norway, in the Pyrenees ,in Stiria, and in Cornwall .

Species II. Earthy Cobalt. Of this there arethe four following varieties.

Var. I. Friable black cobalt, Schwarzer Ko-bolt mulm. Cobalt terreux noir friable.

The colour of this is black, bluiffi, brownilhor greyilh black. It has no luftre, is of a loofeearthy confidence, friable and meagre; it flainsthe fingers in a flight degree, and gives a bright-ilh dreak. It is foluble in muriatic acid, tingesborax blue, and very rarely betrays any fulphu-reous or arfenical ingredient when treated withthe blow-pipe.

Var. 2. Indurated black Cobalt . Verhcerteterfchnvarzer Kobolt. Cobalt terreux noir endurci.

In colour it refembles the former, except thatit is fometimes of a dark greenilh black. It oc-curs maffive, dilfeminated, inveding, kidney-fhaped, cludered or in veins. It is dull, buttakes a polilh by friction. Its fracture is earthyand compaft, paffing into flat conchoidal. Itpoflefies a moderate degree of hardnefs. Sp. gr.from 2. to 4. With nitric acid it gives a redfolution, and a bluilh green one with muriaticacid. It has not been accurately analyzed, butconfids of oxyd of cobalt with a fmall variableproportion of arfenic and fulphur mixed withvitreous filver ore, oxyd of iron and clay.

This and the preceding variety are alwaysfound together, but the indurated is by muchthe mod rare. It is found in Saxony, Thurin-gia, Swabia , and Tyrol.

VOL,. I.

Var. 3. Yellow Cobalt. Gelber Erdkobolt.Cobalt terreux jaune.

Its colour is that of faded draw, paffing intogreyifli-white and often dreaked with brick-red. It is found in mafs, diffeminated, or in-veding. It is without ludre, has a fine-grainedearthy fra&ure, gives an unctuous dreak, is foftand friable.

It is infufible per fe, gives a feeble arfenicalodour, and communicates a deep blue tinge toborax : but when mixed with iron, as it oftenis, the colour is greenifli.

This is one of the rared of the ores of cobalt:it has hitherto been found only at Saalfeld inThuringia, Alpirlbach in Wirtemberg , and Al-lemont in Dauphine.

Var. 4. .Brown Cobalt. Brauner Erdkobolt.Cobalt terreux brun.

Its colour is a clear liver-brown paffing into'grey, yellow, and black. It occurs in mafs ordiffeminated; it is dull, but acquires a greafyludre by friction. Its fracture is fine-grainedearthy. It is eafily broken, being almod friable.It has not been analyzed, but appears to be theconne£ting link between the fecond and third,varieties. When thrown on burning coals itgenerally gives out an arfenical odour.

Sp. III. Red Cobalt. Of this there are twovarieties.

Var. 1. Crydallized. Koboltblute. Fleurs deCobalt .

The ufual colour of this mineral is peach-blofiom red, paffing into cochineal and greyilh-red; by expofure to the air it becomes palerand almod white. It is found very rarely inmafs or diffeminated, and dill feldomer cluderedor kidney-fhaped: its mod ufual date is that ofa thin crydalline covering, or minute drufes ofcrydals. The forms which it generally afteCtsare rectangular tables, or tetrahedral acicularprifms, or hexahedral prifms terminated bydihedral fummits: thefe figures however arenot often determinable on account of theminutenefs of the crydals, and their tendencyto form radiated and globular groups. Thefurface of the crydals is fmooth and brilliant,and their fraCture lamellar. The fradture ofthe other kinds is radiated paffing into fibrous.It is tranflucid, and often when crydallized fe-mitranfparent.

Before the blow-pipe it gives a faint arfenicalodour, and becomes of a dark grey colour, it isalmod infufible by itfelf, and gives a beautifulblue tinge to borax.

Var. 2. Earthy. Koboltbefchlag. Cobalt terreux rouge pulverulent.

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