UNCOMMON SPECIES of ZEOLITE. 303 



The flone which has now been defcribed refembles fome of 

 the varieties of Tremolite mentioned by Saussure *, in the pro- 

 perty of giving a phofphoric light by friction. Its fpecific gra- 

 vity alfo is fomewhat greater than that of the ordinary kinds 

 of zeolite, as ftated by mineralogifts. Excepting in thefe par- 

 ticulars, however, it has the principal characters of a zeolite ; 

 for example, in its internal compofition, in having been found 

 in a whin rock adhering to prehnite, and in producing a jelly 

 with acids. . Tremolites have a higher fpecific gravity than this 

 ftone, are more infufible, and are confiderably different in their 

 compofition f . Befides, fuch kinds of tremolite as I have exa- 

 mined cannot be decompofed by acids, even when boiling, and 

 muft be heated with potafh or foda before their component 

 parts can be feparated ; but the fubftance in queftion is com- 

 pletely decompofed by acids, like the greater number of zeolites, 

 in a very few minutes, and without the afliftance of heat. For 

 thefe reafons, it appears to me to be a zeolite. 



Vol. V.— P. II. R r XIII. 



* Voyages dans les Alpes, 1923. 



f Kirwan's Mineralogy, vol. I. p. 278. Traite de Mineralogie par Hauy s 

 torn, 3. p. 151 and 227. 



