128 EARTHS. ARGILLACEOUS. 37. Lava. 



and Germiny, forming vail mailes, and o/ten broken into j^ 

 4, or 5-fivi<<i prifms: colour greyifi-i, blueifli or purplifh- 

 black, black, blackiih or reddirii-brovvn, and frequently con- 

 taining bafaUine, quartz, cry (lAllized carbon.ue of lime, fel- 

 fp r, and olivin ; hence it is frequently porous, cellular or 

 cavernous, from the decomp ^iition or falling out of thefe 

 ilones: fradlure earthy or fine fplintery, often uneven: it 

 elfervefces a bttle with acids, and may be mdted into black- 

 i!li- green glafs. 



37. LxWA. Confiding of alumina, with a larger 

 portion of filica and oxyde ot iron, -^nd frequent- 

 ly a lir.tle carbonate of lime and carbonate of 

 magnefia: generally of a dull colour, becoming 

 hoary when icraped, meagre, breaking into in- 

 determinate fragments, mouldering into argill in 

 the air: produced by the internal fires of vol- 

 canic mountains from which it is thrown out, and 

 melting again into a black glafs. 



tompatia. Nearly opake, compa6l, hardifh, of a conchoidal texture* 



Compact Lava. Kir ^m an mineral. I. />. 404. 



Compaft Lava. SchmeiJ/er. \.p. 189. Thomfon^ ^. p. 147. 



Found in volcanic mountains and their neighbourhood, appear- 

 ing to have been fufcd by the action of fire, but not vitrified, 

 and becoming when cooled, compadl, clofe, and folid, and 

 bearing the refemblance of its original mineral: colour ge- 

 nerally blackifh, fometimcs grey, brovvri, or red, rarely white, 

 very rarely green or blue : its fub{lance is fo very little po- 

 rous as to admit being cut into flabs with an almoft entire 

 furface, and polilhed like marble; fra6lure earthy or fine 

 fplintery, more rarely foliated : contains ofien hornblend, 

 white garnets, olivin, calcareous fpar, mica, fnorl, &c, 



*vitrea. Diaphanous, fliining, compafi;, hard, of a conchoidal 

 texture. 

 Pumex vitreus. Syji. nat» xxi, 3. /». 182. ». 7. 

 Porus igneus vitreus. Wall.Jyft» z. p. 387. n. 5. 

 Vitreous Lava. Sch/neiJJer mineral. \. p. 189. Kirwan 1,^.401. 

 Compaci glafs. Thomfon cbem, 4. p. 1 50. 



2. Lava with glaffy filaments, 



Hamilt. Phil Tranf. 1780. njol. 'jO. part l,«. 4. 



Found about volcanic mountains in He^w Spaitty Peru, Hecla, 



Vefwviusy and fometimes in places where lubterraneous fires 



have taken place either from pyrites or in coal-pits: contains 



generally other fubllances imbedded, and is more or lefs 



