128 
, <ompa(la. 
’vitrea. 
EARTHS. ARGILLACEOUS. 37. Lav.>. 
and Germany, forming vaft mafies, and often broken into 
4, or 5- Tided |>rifins; colour grcyiili, blueilli or purplifli- 
black, black, black, fh or reddifii-brown, and frequently con- 
taining bafaliine, quartz, crylldlizcd carbonate of lime, fel- 
fpii-, and olivin ; hence it is frequently porous, cellular or 
cavernous, from the decompolition or falling out of thefc 
ftones : Irafture earthy or fine fplintery, often uneven: it 
eftervefees a little with acids, and may be melted into black- 
ilh- green glafs. 
J7. LAVA. Confifting of alumina, with a larger 
portion of filica and oxyde of iron, and frequent- 
ly a little carbonate of lime and carbonate of 
magnefia : generally of a dull colour, becoming 
hoary when ferapeti, 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. 
Nearly opake, conipaH, hardllh, of a conchoidal texture. 
Compafl Lava. Kir~,van mintral. I. p, 404. 
Compaft Lava. SchmeiJJer. p. i8g. Thsmfen, if. p. 147. 
Found in volcanic mountains and their neighbourhood, appear- 
ing to have been fufed by the aftion of fire, but not vitrified, 
and becoming when cooled, compaft, clofc, and fulid, and 
bearing the rcfcmblance of its original mineral; colour ge- 
nerally blackilh, fometimes grey, brown, or red, rarely white, 
very rarely green or blue: its fubftance is fo very little po- 
rous as to admit being cut into ilabs with an almoft entire 
furface, and polilhed like marble ; frafture earthy or fine 
fplintery, more rarely foliated : contains often hornblend, 
white garnets, olivin, calcareous fpar, mica, fhorl, &c. 
Diaphanous, Oiiiiing, compadt, hard, of a conclioidal 
texture. 
Pumex vitreus. Syji. nat. xii. 3. p. 182. ». 7. 
Porus igneus vitreus. Wall.Jyft. 2. p. 387. n. 3. 
Vitreous Lava. SchmeiJJer mineral. \ . p. i8g. KirTvem i.p.^oi, 
Compaft glafs. Thomfon chem. 4. /. 150. 
2, Lava with glafl'y filaments. 
Hamilt. Phil Tranf. 1780. 'vol. jO, part t, a. 4. 
Found about volcanic mountains in iV/au Spain, Peru, Hecla, 
l^efu-vius, and fometimes in places where fubterraneous fires 
have taken place either frora pyrites or in coal-pits : contains 
generally other fubftances imbedded, and is more or lefs ' 
