ITALY. LETTER XI. I4g 



Second Clajfts of Vefuvian Stones and Fojjils, 

 prepared, by fire. 



Before I proceed to the defcription of the 

 lava and other volcanic productions of Vefuvius, 

 I think it convenient firft to fpeak in particular of 

 the fherl-cryitallifations, which are fo common in 

 the lava; and which I believe to be produced 

 by fire, and thus far to be different from thofc 

 which are inclofed in the above micaceous lime- 

 ftone fpar. I have feen the following varieties. 



i. Globular polygone garnet-like cryftals, with 

 fifty-fix for the moft part rhomboidical faces ; the 

 biggeft an inch diameter; either vitreous white 

 tranfparent ; or femi-pellucid lefs vitreous ; or fari- 

 naceous white opaque; and in old lava, friable to 

 a powder which does not effervefce with acids, and 

 is comparable to the white terraceous furface of 

 flints (Cronfted. Mineral, in the note, 40.) In 

 the eldeft lavas, efpecially thofe which have been 

 long expofed to the acid of the air, they are en- 

 tirely dilTolved and changed into clay. Thefe 

 fherls or white garnets * are extremely common in 



* Their nature and form prove them to be true white gar- 

 nets ; but being commonly deilitute of the garnet-hard nefs 

 arid the lava- fherls, whofe fubftance is the very fame, appear- 

 ing under many other forms, I choofe rather to call them 

 garnet-like fherl-cryllals. 



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