crystallized Bodies contained iii Lava. 301 



ibrni. Thus we may say that capillary schorls, or mineral 

 asbestos, resemble cotton or linen threads, although between 

 these two substances there is merely a resemblance of form, 

 without any reality. This remark was necessary, because 

 one might think from the expression " singularly resemble" 

 that there is something more than a mere appearance. 



The tremolite, which derives its name from Val-Tremola, 

 near St. Gothard, one of the principal places where it is 

 found, is a radiated mineral substance, the threads of which 

 are often of a brilliant white, and united in sheaves or bun- 

 dles. These sheaves issue from one centre and diverge in a 

 round form, which gives them the form of a radiating star; 

 and, these cenires being varied, from this there results dif- 

 ferent directions in the rays, the length of which is from 

 half an inch to three inches and upwards. This mineral 

 substance is one of the most curious and agreeable to look 

 at. It is sometimes mixed with talc and calcareous spar, 

 i. e. of two substances, one of which is vltrescible, but of 

 difficult fusion, and the other is calcinable; a circumstance 

 which of itself excludes the idea of the least relation between 

 the tremolite and the produce of the glass-houses : and when 

 we compare these products with the brilliant threads of the 

 trenjolitc, which, taken by themselves, have each the form 

 of a four-sided prism, we must be astonished that such an 

 assimilation has been made. The tremolites are vitrescible 

 but not vitreficd, and never were so. 



Let us, however, turn our attention to such crystallized 

 bodies inclosed in lava to which the vitreous crystallites have 

 been assimilated. I can make this comparison upon a o-reat 

 number of pieces, which I collected in burning and cxtiu- 

 guished volcanoes. 



The lavas which contain leucites, or white granates, also 

 frequently contain pyroxdne volcanic schorls, and crysolites 

 or olivines *. Here there are two kinds of crystals, very 

 distinct from each other by their form and colour, contained 

 in the same lava, surrounded by the same crust, which in 



• I shall afttrwaids designate these sehorTs by the name of pyroxene scJiorls, 

 because the simple denomination of pyrortncs i}oe» not belong to them exclu- 

 lively ; :iU the budics C(.:itaincd ia ]ava« being aku pyroxeucs, i, e. strangers 



Ui Utt. 



itself 



