EARTHS. ARGILLACEOUS, 37. Lava. 129 
tranfparent : colour generally black, rarely cinereous, green- 
ilh blueifh, or white, fometimes prifmatic : ulually of a 
common, rarely of a llalaaiiical globular or pyramidal form: 
melts with more difficulty than other Ipecies, on account of 
its containihg lefs iron, carbonate of lime and magnefia ; is 
frequently fo hard as to llrike fire with fteel. 
‘^<"-tacedi Veficukr, roughj Hiining irifernally, of a conchoidal tex- 
ture. 
Volcanic fcoria and flaggs. Kirwan miner, i. /. 402. 
Spongy Lava. Schmeijier miner. \ .p. 189. 
Scoria. 'Thomfon them, 4. p- 149 ' 
Porus igneus lapideu.s. WalLfyU. a. p. 227, «. 3. b. 
Found in flreams of volcanic lara, generally covering the 
Lava compada, black or brown, with often a mixture of he- 
tergeneous matters : the furface appears full of empty bub- 
bles, often difpofed in an undulate manner. 
forosa^ Opalce, without luftre, porous, lightilh. 
Cellular Lava. Kirnnan mineral. 1 . p. 403. 
Porous Lava. ScbrdeiJJer mineral, l. p. 189. 
Porous Lava. Hhornfan chem. p. 149. 
Found in volcanic mountains and their neighbourhood, more 
rarely in thofe which have been cxiinguilhed, and feems ra- 
ther to have been thrown from the crater tban run over at 
the fides : colour black or brown, fometimes reddiffi-browh: 
it probably contains more carbonate of magnefia than the reft, 
and is more fubjea to deftruftion than compaa lava: its 
pores are larger near the furfacc than towards the centre, 
Opake, without luftfe, parallel, fibrous, porous, light, 
rough. 
Pumex vulcani. SyU. nat. xii, 3. /. 181. n. l. 
Porus igneus lapideus. Wall. Jyst. 2. p. 37 S‘ 
Pumice. Kir-wan miner, l . />. 41 5. ‘Ihom/on Chem. 3. p. 1 49. 
Fumice-ftone. Schmeiffer mineral. I. p. 188. 341. 
1. Fibrous, with elongated pores. Kirnuan. var,\. 
2. Pores very minute, hardly fibrous. Kir^wan. -var. 2, 
Found in the afties of lUoft volcanic mountains, from whence it 
is wafhed down into the fea : colour grey, greyiih-white, 
brown. Of reddifti, rarely ycllowifti : the fibres are gener !ly 
parallel, more or Icfs difcernible, and have a filky luftre : 
does not effervefee with acids, melts into a white enamel ; 
contains filica 77,50. alumina 17,50. oxyde of iron i.yji 
foda of potafs 3,00. Klaproth, 
Originating from fiibftances which have been ignited by- 
burning Itrata of foffile coals. 
VUL. Vll. — R 
