EARTHS. ARGILLACEOUS. 37. Lava. 



12^ 



tranfparent: colour generally black, rarely cinereous, green- 

 ifh, blueidi, or white, fometimes prifmatic: ufually of a 

 common, rarely of a Ilala6\iiical globular or pyramidal form: 

 melts \\ ith more difficulty than other fpecJes, on account of 

 its containing lefs iron, carbonate of lime and magnefia : ii 

 frequently io hard as to ilrike fire with (leel. 



scsriacea, Veficular, rough, (liining internally, of a conchoidal tex- 

 ture. 



Vohanic fcoria and flaggs. Kirnuan miners l, p, 402. 



Spongv Lava, Schmeifier miner. \, p. 1 8g, 



Scoria, Thomfon chenix 4. p. 149. 



Porus igneus lapideus. Wall, fyH^ 2. p» 227, n. 3. b. 



Found in dreams of volcanic lai-a, generally covering the 

 Lava compafta, black or brown, with often a mixture of he- 

 tergeneous matters : the furfate appears full of empty bub- 

 bles, often difpofed in an undulate manner, 



Opake, without luftre^ porous^ lighti(h. 



Cellular Lr.va. Kirv^an 7nineral. lv/>. 40:5. 



Parous Lava. SchmeiJJer mineraU I. />• i8g. 



Porous l.ava. Ihomfon chem, ^. p. 149. 



Pound in volcanic mountains and their neighbourhood, rnore- 

 rarely in thofe which have been extinguifhed, and feems ra- 

 ther ro have been thrown from the crater than run over at 

 the fides : colour black or brown, fometimes reddifh-brown: 

 it probably contains more carbonate of magnefia than the r»;ft, 

 and is more fubjecl to dellrudlion than compad lava ; its 

 pores are larger near the furface than towards the centre. 



Opake, without luflre, parallel, fibrous, porous, light, 

 rough. 

 Pumex vulcani. Syfi. nat. xii. 3. />, 181. «. i. 

 Porus igneus lapideus. Wall.jyst. z. p, 375. «. 2, 

 Pumice. Kir~L<jan miner, i. p, 41^. Thotn/onChem^ 3. p, 149, 

 rumice-ftone. Schmeijfer trJneraL l. p, 1S8. 341, 



1. Fibrous, with elongated pores. Kirnvan. ^var, i. 



2, Pores very minute, hardly fibrous. Kiriuan. var. 2* 



Found in the allies of moft volcanic mountains, from whence ir 

 is wafhed down into the fea ; colour grey, greyifh-whiie, 

 brown, or reddilh, rarely yeilowiih : the fiores are generally 

 parallel, more or lefs dilcernible, and have a filky luftre : 

 does not elfcrvefce with acids, melts into a white enamel: 

 contains filica 77,50. alumina 17,50, oxyde of iron 1,75, 

 foda of potafs 3,00. Klaproth* 



Originating from fubflances which have been ignited by 

 burning itrataof foiliit' coals. 



VOL. Vil. — R 



