15© EARTHS. SILICEOUS. 44. Feldrpatum. 



44. FELDSPATUM. Confifting of the greater 

 part filica, Ibme alumina and potafs, and a very 

 fmall quantity of lime and oxyde of iron : hard, 

 iightifh, fhining, lamellar, breaking into frag- 

 ments which prefent 4 faces, mouldering into 

 argil, parafitical: not effervefcing with nitric 

 acid, eafily melting without ebullition into la 

 pellucid glafs. 



fubicum^ Redd ifh -brown, of a glaffy luftre, and fomewhat fplin- 



tery fradure, breaking into cubic fragments which 

 are not fpecular, falling fpontaneoully into cruftofe 

 fragments. 

 Pe'^rilite, Cubic felfpar. Kirn.van miner. \.p. 325. 

 Four.d, though rarely, in Saxony, of a comrnon form, diapha- 

 nous or f mewhat opake : fragments cubic or inclining to 

 that form, the faces of which are not poliflied : is very brit- 

 tle, ..nd at 160° of heat whitens and concre'tes without any 

 farther fign of fufion : fpecific gravity 3,081. 



vulgare. Of a glafly luftre and foliated texture, breaking into 

 rhomboidal fragments with 4 fpecular faces. 

 Spatam fixiim fcintillans. Syst* nat. xii. 3. p. 153, «. 6. 

 Spatum fcintillans. Cronft. miner. 66. H. 

 Spatum durum. Wall.mtn.6i» 

 Common Felfpar. Kirtvan mineral. I. ^. 317. 

 Common F.ellpar. SchmeiJJer mineral. 1.^.132, 

 Common Felfpar. Thomjonchem, 3. /. 554. 



1. Opake. 



Spatum campeftre. Syst. nat. xii. 3. /, 50, n. i 2. 

 Spatum fcintillans. Wall, fyst, miner. \, p. 205, n, I« 



2. Tranfparent. 



Spaium lilicum. Syji^nat. xii. 3./. 50. «. 13. 

 Spatum fcintillans. V/alL/yst, min, l. p. 206. «. 2. 



3. Of a common form. 



4. In the form of cryllals. 



" Spat, fcintill. cryQallis. Wall.fyst, i. p> 207. n. 3, 

 Spat, fcintill. druHcum. Cronst, mineral. 66. 2. < 



^. The cryftals prifmatic. 

 The prifms acicular. 



b. The cryftals parallelepidid, 



p. The cryftals thicker, with the fides more equal, 



Iri 4-fided right angles. 



In 6-fided right angles. 



