MINERALOGY. 



rounded ; fometimes four prifms are arranged in the form of 

 a crofs. The prifms appear compofed of two diilintt 

 fubttances, as if they had once been hollow, and thefe 

 hollows filled up with clay -date, nearly fimilar to what the 

 cryftals are imbedded in. The exterior part of the prifm 

 is of a greyifh-white or reddifh colour, and varies in thick- 

 nefs, in fume fpecimens being a mere fhell ; within this, 

 is a dark-blue or black prifm, exactly parallel to that by 

 which it is inclofed. Frequently from each angle of the 

 interior prifm a black line or thread proceeds, bifefting 

 the corr&fponding angle of the white prifm, and often ter- 

 minated by a fmall black prifm. The wliite part exhibits 

 a lamellar iiruiElure, parallel with the lateral planes of the 

 prifm : it has a flight gliftening luftre, is tranflucent, and 

 fcratches glafs. The fpecilic gravity is 2.9. Before the 

 blow-pipe, it fufes into a whitilh fcoria ; the black part 

 affords a black glafs. This mineral occurs in acicular 

 cry ftals in fome beds of dark flate in the mountain Skid- 

 daw, Cumberland. The largeft cryftals are found in clay- 

 flate, near St. Brieux, in Brittany. Some mineralogiils 

 confider chiaftolite as the lame fubftance as andalufite ; 

 others clafs it with common felfpar, and fome regard it as 

 a diftinft fpecies. 



Chlorite, Talc chlorite, Haiiy. This mineral is nearly 

 allied to talc and mica. The prevailing colour is various 

 ihades of green ; hence it derives its name from the Greek 

 k7x:^o:, gfeeii. It is divided by profefior Jamefon into four 

 fub-fpecies : earthy chlorite, common chlorite, flaty chlorite, 

 and foliated chlorite. 



Earthy Chlorite occurs maflive and diffeminated, and in- 

 crufting other minerals, and inclofed in dendritical forms 

 in adularia and rock-cryftal. It confifts of fine fcaly par- 

 ticles clofely adhering, and has a glimmering or ghilening 

 pearly luftre, and feels rather greafy. The green colour 

 becomes lighter in the ftreak. The fpecific gravity is 

 2.6. Before the blow-pipe, it melts into a blackifh flag. 

 According to Vauquelin, the conftituent parts are, 



Silex 

 Alumina 

 Magnefia 

 Muriate of foda | 

 and potaih j 

 Oxyd of iron 



26.50 



18.50 



8.00 



43.00 

 98.00 



According to Haiiy, the fcaly particles are regular 

 hexagonal prifms when viewed with the microfcope. 



Common Chlorite is a leek or dark-green colour, inter- 

 mixed with black. It occurs in rocks of various kinds, in 

 beds and veins, either alone, or with quartz, magnetic 

 iron-ftone, iron-pyrites, hornblende, aftinolite, and other 

 minerals. It is amorphous, has a glimmering luftre, an 

 earthy frafture, and a fine granular, laminated, or fcaly 

 ilrudture. Common chlorite is foft, opaque, and greafy. 

 Its fpecific gravity is 2.8. It occurs in various parts of 

 Scotland, and in Cornwall, Cumberland, and all alpine 

 parts of England. 



Foliated Chlorite: Talc chlorite, Haiiy. — Its colour is 

 leek-green: it occurs cryftallized in fix-fided tables, curioufly 

 aggregated in cyhndrical or conical forms. The cryftals 

 are longitudinally ftreaked. The luftre is refinous, either 

 gliftening or ft^ining. The ftrucl;ure is curvedly lamellar, 

 with a fingle cleavage. It is opaque or tranflucent at the 

 edges ; it is foft, fettile, and rather greafy. The fpecific 



gravity is 2.8. According to Larapadius, the conftituent 

 parts are, 



Silex - . . ,- 



Alumina - . . jg 



Magnefia - . . ,3 



Iron - - - 10 



Water ... 3 



105 



Foliated Chlorite is found in various parts of the con- 

 tment of Europe, and on the ifland of Jena, one of the 

 Hebrides. 



Chlorite Slate^ has a greyifli or darkifh-green colour ; it 

 occurs in beds in clay -flate, fometimes aflociated with talc- 

 flate, into which it pafTes. It has a gliftening refinous 

 luftre, a flaty fl;ruaure, inclining to fcaly. On minute 

 examination, it appears compofed of fmall fcales of chlorite 

 clofely adhering. Chlorite-flate forms beds in mountains 

 of clay-flate in various parts of tlie Grampian-hills. It 

 pafles into hornblende-flate and clay-flate. The fpecific 

 gravity is 3.03. 



CHLOROPirAXE, a variety of flnor fpar from Siberia, 

 which gives out a beautiful' apple-green light when placed 

 on a heated iron. PaUas mentions a pale-violet blue variety 

 fpotted with green, which becomes phofphorefcent when 

 held in the hand, and gives out a pale-whitifli light ; in 

 boiling water, it emits a green light, and at a'' higher 

 temperature a blue light. See Fluor Spar. 



CnROMATE of Iron, Fer chromate, Fr. has a pitch-black 

 colour, with fomewhat of an olive tinge fiiperficiallv. 

 It occurs maffive and difleminated, and alfo cryftallized 

 in oftahedrons. It has a fliining Inftre, between refinous 

 and metallic. The frafture is uneven, or imperfeftly 

 fm.all conchoidal, and fometimes imperfeftly lamellar. It 

 fcratches glafs, is opaque. The colour of the ftreak is afli- 

 grey or brownifli. The fpecific gravity is 4.03. It is 

 rarely magnetic, is infufible, but tinges borax of a beautiful 

 green colour. According to Vauquehn, the conftituent 

 parts are, 



Chrome of France. 

 Oxyd of chrome . . ^ 5 



Oxyd of iron " * 35 



Alumine . - . 20 



Silex ... 2 



According to Klaproth, 



Chrome of Stcria. 

 Oxyd of chrome 

 Oxyd of iron 



Alumine . . . 



Silex 

 Lofs by heating 



5S 

 33 



Chromate of iron occurs in beds and veins, and in im- 

 bedded maffes, in ferpentine and talc -.late. It has been 

 found at Portfoy, in Bamfshire, and is faid to occur in 

 confiderable qnantities in the Shetland iflands. It occurs 

 in the vicinity of Nantes, and in the department of Van. 

 The greateft quantity lias hitherto been found in fer- 

 pentine, in the Bare-hills near Baltimore. The chromic 



acid 



