MINERALOGY. 



It appears to be common or femi-opal rendered opaque 

 by the great intermixture of oxyd of iron. 



OaiEN'TAL Amethyjl, Sapphire, Ruby, Topaz, and 

 Emerald, names given by jewellers to varieties of the fapphire. 

 The blue fapphire is the true or oriental fapphire; the 

 violet-blue is the oriental amethyjl ; the red fapphire, the 

 oriental ruby ; the yellow fapphire, the oriental topaz ; and 

 the green fapphire, the oriental emerald. See Sapphire, &c. 

 Orpimext, Red, or Realgar, Sulphuret ofArfenic; Arfenie 

 fulphuree rouge, Fr. (See Arsenic.) According to Kla- 

 proth, the compofition of this ore is, 



Arfenie - - - 69 



Sulphur - - - 31 



100 



Orpimext, Telloiu, is compofed, according to Kla- 

 proth, of 



Arfenie - - - 62 



Sulphur - - - 38 



100 



Osmium occurs as a native alloy of the metal fo 

 called with iridium ; it is found in grains along with 

 platina in alluvial foil in South America. The greens 

 have a pale fteel-grey colour, a metallic lullre, and lamel- 

 lar ftruClure ; it is harder than platina, and brittle. The 

 fpecific gravity is 19.5. By fufion with nitre, it ac- 

 quires a dark-black colour, but regains its luftre and 

 colour by heating with charcoal. 



Palladil'm is a native alloy of the metal palladium, 

 with a minute portion of platina and iridium ; it occurs in 

 grains along with grains of platina in the alluvial gold 

 diftrids in Brazil. Its colour is pale-fteel gi-ey palling 

 into filver-white ; the ftrufture of the grains is divergingly 

 fibrous, the luftre metalhc. The fpecific gravity is 12.148, 

 liowry. Palladium is infufible ; but on the addition of 

 fulphur, it melts with eafe by continuance of the heat, 

 the fulphur is diffipated, and a globule of metallic pal- 

 ladium remains. With nitric acid, it forms a deep-red 

 folution. 



Paranthine. See Scapolite. 



Pearl-Spar. (See Brown Spar, y^(/</fn^(!.) The name 

 pearl-fpar has been given to thofe varieties of this mineral 

 which in colour and luftre have a ftrong refemblance to 

 pearl, but it often occurs brown, black, and of various 

 colours. 



Pearl-Stoxe, Lai'e vitreufe perlee, Haliy. ( See Pearl- 

 Stoxe.) This mineral is regarded by many mineralogifts 

 as a volcanic production ; it is frequently intennixed with 

 obfidian, and hence is clafled by them as a variety of the 

 latter mineral. It occurs in bafaltic and porphyritic rocks, 

 in large and fomewhat angular concretions, which are com- 

 pofed of fmaller roundilh concretions, and thofe of others 

 ftill fmaller. The furface of the concretions is fmooth, 

 fliining, and pearly. The colour is grey, paffing into 

 pearl-grey and greyifh-black. It is tranflucent on the 

 edges ; it fcarcely fcratches glafs, is eafily frangible, and is 

 fufible with intumefcence before the blow-pipe into a white 

 fpongj' glafs. This mineral has been found near Sandy Bras, 

 in Ireland, in the ifland of Iceland, and in Mexico ; it was 

 firft difcovered in Hungary, where it occurs in large beds. 

 It is clafled by Mr. Jamefon and Werner with obfidian, 

 pitch-ftone, and pumice, as forming a member of the 

 pitch-ftone family. 



Pea-Stone, Pifolithe, Fr. This mineral is compofed of 



carbonate of lime, flightly coloiu-ed yellowifh-white or 

 brown by the oxyd of iron ; it is properly a calcareous tufa, 

 containing rounded globules, varying in fize, from a pea to 

 a hazel-nut ; thefe confift of concentric lameUx, and often 

 contain in the centre a minute fragment of quartz, felfpar, 

 or granite, and fometimes, but rarely, a double fix-fided 

 pATamid of rock-cr^^ftal ; but in fome inftances, the centre 

 of the globule is hollow. Pea-ftone occurs in great mafles 

 in the vicinity of the hot fprings at Carlfbad, in Bohemia ; 

 its formation we conceive to be analogous to that of 

 roe-ftone, and to be the refult of cryftallization ; the par- 

 ticles included having difpofed the calcareous matter to 

 cryftallize round them, in the fame manner as a thread or 

 fragment of a ftone in a faline folution, generally difpofes 

 the crv'ftals to (hoot round them. 



Pergasite, the name given to a new mineral found at 

 Erfby, near Abo, in Finland. The following imperfect 

 account is the only one we have of its character. It has a 

 green colour ; its form is an o£tahedron, with a cleavage in 

 three direftions ; it is harder than fluor fpar. The fpecific 

 gravity is 3.1 1. Before the blow-pipe, it melts into a mafs 

 with a pearly-white luftre. Its conftituent parts are given 

 as under : 



Silex .... 



Magnefia .... 



Lime .... 



Alumine . - . - 



Oxyd of iron 



of manganefe 



— — - of an unknown metal 



Fluoric acid and water 

 Lofs - . . 



42.10 

 18.27 

 14.28 

 14.08 



3-52 



1.02 



0-33 

 3-9° 

 2.59 



100.09 



t'ERiDOT ChryfoUte. See Chrysolite and Olivixe. 

 Petalite, a mineral recently difcovered in Sweden ; ex- 

 ternally, it nearly refembles fome varieties of quartz, but the 

 cleavage is two-fold, parallel to the fides of a rhomboidal prifm ; 

 two of the planes are fplendent, and two dull. The planes 

 meet at angles of 100° and 80°, forming a four-fided prifm 

 with a rhomboidal bafe. Its colour is white with a flight tint 

 of pink ; it fcratches glafs, but yields vi-ith difficulty to the 

 knife. When expofed to the flame of a blow-pipe it remains 

 for fome time infufible, but by continued heat it exhibits a 

 glazed furface, which, on examination with a lens, appears 

 full of minute bubbles. When triturated, the powder has 

 the whitenefs of fnow. It is partially foluble in highly con- 

 centrated nitric acid, lofing its colour, and changing to a 

 dingy hue ; the acid at the fame time becomes clouded. 

 The prufliated alkali threw down a green precipitate, and 

 the folution afliimed an amethyftiiie colour, which afterwards 

 changed to brown. The conllituent parts of this mineral 

 are ftated to be, 



Silex 80 



Alumine .... 15 



Manganefe .... 3 



And a new alkali ... 2 



This alkali proves to be the oxyd of a new metal. The 

 new alkali has been called hthia and lithion ; it has a greater 

 capacity of faturating acids than any other alkah, and forms 

 a clafs of falts that are remarkably dehquefcent. With 

 alcohol, lithion yields a rofe-coloured flame, like that com- 

 municated by ftrontian. The metal of lithion bears a ftrong 

 refemblance to fodium. The alkali found in petalite con- 

 tains 44.84 oxygen, united to a metalhc bafe. 



Petroleum, Liquid Bitumen, or Mineral Oil. (See 



Bitumex.) 



