MINERALOGY. 



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PvcNlTE. ) The cry ftals of this mineral are long hexahedral 

 JS, anJ are deepl\ llreaked longitud.nally They have 

 a cleavage at right angles to the axis of the pufm. Fycnite 

 Tnovv confidered by HaUy as a variety of the topaz. 



Pyrites. See Pyriths. . 



Pyrope. This mineral is now regarded by Hauy as a 

 variety of the precious garnet, with an accidental portion of 

 ^agndia derived from the rock in which it is imbedded. 



Pyrophysalite. See Pyrophysalite. 



Pyrosmali«. Native muriate of iron. See Iron- 



"" P^'RolSf Augit. See Pyroxekk and A.oix, A.l- 



'^"quartz, Quar. hyahn, Fr See Quartz 



Common (l^Tar,:, Rod CM Ametbyjl and Catrngorm 

 Stone, or cTove-bro^n Quart-., Jventun,. Q«nrt. ^ndRofe 

 or MM Quarts, are efientially the fame mineral fubftance 

 or pure fdex, varying only in tranfparency or colour, owing 

 nrobably to a very flight admixture of the other earths or 

 metallic oxyds, an admixture which may be regarded as 

 accidental, and which is fcarcely appreciable by chemical 

 analyfis. According to Bucholz, rock-cryftal is compofed 

 of 994 of filex. It is probable, however, that many mi- 

 nerals,' which have hitherto been clafl'ed with quartz from 

 bearing in many charafters a clofe refemblance to it, may 

 contain other ingredients befides filex in fuch proportions as 

 to conftitute them diftinft fpecies. This opinion is rendered 

 more probable from the recent difcovery of a mineral in 

 Sweden, called petalite, which might eafily be miftaken for 

 a variety of quartz, but which contains a confiderable por- 

 tion of alumine, and two parts in the hundred of an alkali 

 heretofore unknown. See Petalite, Addenda, and Rock- 



Cr^ftal- 



Quicksilver. See Mercury, Ores of. 



Realgar. See ARSENic-Or«, and Realgar. 



Red Antimony Ore. (See ANXIMONY-Orw, and Red 

 uinthnony.) A variety of red antimony-ore, called tinder- 

 ore, is defcribed by Mr.Jamefon as occurring in delicate 

 flexible leaves, which are opaque and friable, foil ftrongly, 

 and fwim on water. Tinder-ore contains a portion of 

 filver. 



ViTLVt Colalt-Ore. ( See CoBALT-Orfj.) This fpecies of 

 ore is divided by Mr. Jamefon into three fub-fpecies, earthy 

 red cobalt-ore or cobalt ochre, Jlag red cobalt ochre, and radi- 

 ated red cobalt-ore or cobalt bloom ; Cobalt arfeniate aciculaire, 

 HaiJy. The analyfis of this ore by Bucholz gives 



Cobalt 39 



Arfenic acid - - - - 38 



Water 23 



This ore has been found at Alva, in Stirlingfhire, and at 

 Tyndrum; alfo in lime-ftone in Linlithgovvfhire, and at the 

 Dolcoath mine in Cornwall. Slaggy red cobalt ochre has 

 a muddy crimfon-red colour, or dark hyacinth-red, which 

 pafTes into chefnut-brown. It occurs in thin crufts, and 

 ibmetimes reniform. It has a fliining and refinous luftre, a 

 €onchoidal frafture, and is tranflucent, foft, and brittle. 



Red Iron-Jlone. See Iron-ores, Addenda. 



B.ED Lead-ore, or Chromate of Lead. See Lead-ores. 



Red Manganefe-ore. See Manganese. 



Red Silver-ore, or Ruby Silver, where read — before the 

 tlow-pipe on charcoal. 



Reddl|^ Red Chalk, or Red Ochre. See Reddle. 



Retinasphaltum. See Retinasphaltum. 



Reussite, the name given to a fait which occurs in the 

 country round Sedlitz, and at Piln near Brux. It forms a 

 mealy efflorefcence, and is alfo cryftallized in flat fix-fided 

 prifms and in acicular cryftals. According to Reufs, it 

 confills of 



Sulphate of foda - - 66.04 



Sulphate of magnefia - 31-35 



Muriate of magnefia - - 2.19 



Sulphate of lime - - 0.42 



Rhomb Spar. See Browx Spar, Addenda. 



Rock Butter. (See Rock Butter.) This mineral appears 

 to be a fub-fulphate of alumine. It oozes from aluminous 

 rocks. 



Rock Cork ; AJheJle Trepe, Haiiy. See Rock Cork. 



Rock-crystal. (See Quartz.) This is the purefl; 

 variety of quartz. Very large and brilliant rock-cry ftals 

 occur in various parts of Scotland. The fmoke-grey or 

 clove-brown cryftals are called cairngorm, from a place ia 

 the upper part of Aberdeenfliire, where they occur in allu- 

 vial foil along with beryl and topaz. The largeft rock- 

 cryftals hitherto found come from the ifland of Madagafcar. 

 Faujas St. Fond mentions a cryftal imported from thence 

 into France, which weighed upwards of one hundred and fifty 

 pounds. Very brilliant groups of rock-ci-yftal occur in 

 Dauphiny. Vafes of rock-cryftal were highly prized by 

 the ancients. A vafe, broke by the emperor Nero in a fit 

 of defpair, was eftimated at 15,000 livres. Different colours 

 may be communicated to rock-cryftals artificially, by heat- 

 ing them and plunging them into different-coloured folu- 

 tions. 



Rock-salt. (See Rock-salt.) According to the 

 analyfis of Dr. Henry, the rock-falt of Chefhire contains, 

 in 1000 parts. 



Muriate of foda - - - 9834 

 Sulphate of lime 

 Muriate of magnefia 

 Muriate of lime 

 Infoluble matter 



Rock-wood, or Ligniform Afbeflus. See Asbestus. 



Roe-stone, or Oolite; Chaux carbonatee globuliform, 

 Haiiy. See Roe-stone. 



Rose Quartz, or Mili Quartz. See QuARTZ. 



Rubellite, called Red Schorl, a variety of tourmaline. 

 See Rubellite, and Tourmaline. 



Ruby, Oriental, or Red Sapphire. See Gems, and Sap- 

 phire. 



Ruby Spinelle. (See Gems and Ruby.) The fpinel 

 ruby is the common ruby of the jewellers. It differs from 

 the oriental ruby in the form of its cryftallization, and 

 contains a portion of magnefia and chromic acid. The 

 former is nearly unmixed alumine. When thefe two gems 

 are cut, it is, however, difficult to diftinguifti them. The 

 oriental ruby is harder than fpinel. Though the prevailing 

 colour of the common ruby or fpinel is red, yet it is fome- 

 times blue -green or yellowifti-brown. The carmine-red is 

 called the fpinel ruby ; the cochineal ruby is called the 

 balais ruby, from Balachan, the Indian name of Pegu, 

 where it is found. The fpecific gravity varies from 3.50 to 

 7.30 ; that of oriental ruby from 3.97 to 4.28. The latter is 

 a true fapphire. 



ROTILE, 



