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CERUSSE OF ANTIMONY is a perfeftox yd of antimony prepared by nitre. See An-timony.
Of this mineral there are two fubfpecies.
i. Subfpecies. Common Chalcedony. Ge~■tneinerKalzedon,Werner. Calcedoine , Fr. Quartzagaihe calcedoine. Hauy.
The colour of chalcedony is bluifh grey, pafs-ing into milk-white and fmalt-blue •, greenifhgrey, palling into apple and olive green; andyellowilh grey, palling into wax and ochre-yel-low, yellowilh and blackilh brown, and brownilhblack. Two or more of thefe colours are notnnfrequently found in the fame fpecimen, ofwhich one generally forms the bafis, while theothers are diftributed over its furface in dots,clouds, or ftripes: when white and yellowilhbrown ftripes, alternate with each other, theftone is called an onyx, and is highly efteemedby the lapidaries. The grey varieties, with thickprifmatic diftindf concretions, when tranfverfelycut, prefent iridefcent colours when held to thelight, and have hence been named rainbowchalcedony. The tranllucid milk-white varietyis called cacholong. The green and fmalt-bluevarieties are the rarelt; the dark coloured oneswhen cut thin and held to a ftrong light, appearblood-red.
It is found maflive, forming veins, in roundballs of various fizes, called geodes, alfo kidney-Ihaped, botryoidal, ftaladtitic, mamillated, andimpreffed by various organized bodies, fuch asturbinites, &c.: certain cryftalline forms, efpeci-ally thofe of quartz have alfo been attributed tochalcedony, but thefe appear to be nothing morethan cryftals of quartz coated over with chal-cedony. It poffeffes little or no luftre. (Itsfracture is perfectly even, palling into fine fplin-tery and flat conchoidal. It breaks into in-determinate fharp-edged fragments. It fre-quently exhibits concentric lamellar or angulardiftindt concretions. It is commonly femitranf-parent y but the darker coloured varieties areonly tranllucent. It is fomewhat harder thanflint, and by no means fo eafily broken. Sp.gr. 2.58 2.65. It is infufible per fe before theblowpipe, but becomes milk-white and opake.According to Bergman the chalcedony fromFerroe confills of84. Silex
1 6. Alumine, and a little iron
100
It occurs in geodes and veins in Amygdaloid}alfo in veins accompanied by quartz, pyrites,&c. in porphyry. It was anciently procuredfrom Chalcedon in lefier Afia, whence its name,but at prefent is found principally in Scotland and the adjoining iflands, in Cornwall, Iceland ,Saxony, Hungary , Piedmont, and various partsof Afiatic Ruflia.
2d Subfpecies, Carnelian . Karniol, Werner.Carnaline, Fr.
The ufual colour of this mineral is blood-red,whence it paffes into flefh-red, reddifh-white,milk-white, orange, and honey-yellow: two ormore colours often occur in the fame fpecimen,difpofed in zones, ftripes, and arborizations.It occurs in veins and rounded pieces; has aconchoidal fracture and a flight degree of luftre.In other refpedts it agrees with common chal-cedony. The variety with alternate white andred ftripes, is called Sardonyx. Carnelian isfound in various parts of Europe , but the moltbeautiful and valuable pieces are brought fromArabia, and Surat, and Cambay in India . Car-nelian from its beauty and hardnefs, has alwaysbeen much fought after by lapidaries, fome ofthe fineft antique cameos are formed of it.
It is cuftomary among modern mineralogiftsto place agate as an appendage to the fpecies ofchalcedony, fince it is to this mineral that theformer is indebted for its moft ftriking charac-ters, and becaufe the coloured chalcedonies pafsimperceptibly into agate.
Agate is a mixture of chalcedony, carnelian,jafper, hornftone, quartz, heliotrope, amethyft,and indurated lithomarga, aggregated into bi-nary or more complex combinations. It hasneverthelefs feveral charadters by which it maybe diftinguifhed from other minerals.
Although it confifts of parts differing fromeach other in colour and tranfparency, yet thefepoffefs a certain uniformity of arrangement,and Aide into each other by fuch nice grada-tions, as {how them to have been all of fimul-taneous formation. As it differs in the colourof its conftituent parts, fo it does alfo in theirtranfparency; it is never wholly opake likejafper, nor tranfparent like quartz cryftal: ittakes a very high polifh, and its opaker partsufually prefent the appearance of dots, eyes,veins, zones, clouds, bands, or ramifications.
It is found in the form of irregular roundednodules, from the fize of a pin’s-head to morethan a foot in diameter, or in veins or ftrata,and fometimes ftaladtitic. Several varieties ofagate are diftinguifhed by lapidaries. The fine*
Eramerling, Brochact, Kir wan, Havy.