1819.] Scientific Intelligence. 67 



resembling that of Cornwall. The ruby oxide is particularly 

 remarkable in the cavities of the piece. 



IV. Fibrous Prehnite. 



The variety of prehnite which occurs so abundantly in the 

 neighbourhood of Glasgow, is of the fibrous kind. Its specific 

 gravity is greater than that of foliated prehnite, being 2-901. It 

 does not break so readily as the foliated variety. I have not 

 been able to satisfy myself whether it be harder. Its colour is 

 apple-green, and it is composed of fibres which radiate from 

 several different centres. I had the curiosity to analyze a speci- 

 men of it, in order to compare it with the foliated variety, the 

 only one hitherto, I believe, subjected to analysis. The result 

 was as follows : 



Silica 43-60 



Alumina 23-00 



Lime 22-33 



Oxide of iron '.'. 2-00 



Water 6-40 



Loss 2-67 



100-00 



This result approaches very nearly that obtained by Gehlen 

 from a variety of prehnite from Ratschinke. He does not 

 describe the specimen ; but from its specific gravity, 2-924, I 

 think it probable that it was similar to our Glasgow prehnite, or 

 that it belonged to the fibrous variety. Its constituents, as he 

 obtained them, were as follows : 



Silica 43-00 



Alumina 23*25 



Lnne 26-00 



Oxide of iron 2-00 



Oxide of manganese 0-25 



Magnesia, a trace — 



Volatile matter 4-00 



Loss 1-50 



100-00* 



It seems probable, from the preceding analysis, which icnust 

 be nearly exact, that fibrous prehnite is a compound of one atom 

 of silicate of alumina and one atom of bisihcate of lime. Its 

 symbol, then-fore, will be A / S + C S-. Foliated prehnite 

 seems to contain a greater proportion of alumina, and a smaller 

 of lime, at least if Klaproth's analysis ba considered as accurate. 



* Sclmriggir's Journal, iti. 1S6. 



e2 



