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by naturallfts. It confifts of minute cry- 

 ftals, extremely clear and bright, which, 

 having facets in every part, vividlyrefled: the 

 light, and fparkle like fo many diamonds. 

 Thefe are very numerous in the cavities of 

 the fame lava ; but are unequally diftributed, 

 as fome cavities contain but one of thefe 

 cryftals, while others have two, and others 

 three, though the latter are rare. The 

 largeft do not exceed a line, and the moft 

 minute are fcarcely a quarter of a line. 

 While they remain in the lava, it is not eafy 

 to examine them as might be wi(hed ; but 

 many of them may be extracted without 

 injury, and viewed, in every part, with the 

 lens, at leifure. We then perceive that thefe 

 zeolites, where they reft on the lava, are flat ; 

 but in their upper part incline to a globofe 

 figure ; and that, there, their cryftallization 

 is apparent : that the ifolated cryftals, I 

 mean thofe which in their formation grew 

 without attaching to the other cryftals, have 

 eighteen facets, for the moft part pentago- 

 nal, or tetragonal, but never triangular : that 

 thefe ifolated cryftals are extremely rare; 

 the greater number being aggregated^ that 

 F 2 is. 



