Chemical Examination of Stilbite. 75 



26. STILBITE AND HEULANDITE. 



The stilbite of Ha ly has of late years been subdivided into 

 two species ; viz. stilbite and Heulandite. They had been 

 already subdivided into foliated and radiaied zeolite by Wer- 

 ner, wiio recognized the distinction. Mr. Brooke first showed, 

 that tlie angles of the two minerals are different. M Walm- 

 stedt, Professor of Chemistry at Upsal, first showed that the 

 chemical composition of the two is different. 



A pure crystalized specimen of red stilbite, from the rocks 

 near Dumbarton, analyzed in my laboratory, was found com- 

 posed of, 



Silica, - 52-500 



Alumina, _____ 17'36S 



Lime, 11-520 



Water, - 18-450 



99-838 



This mineral has been often analyzed in my laboratory, 

 for it is generally one of the first minerals, (from its easy 

 management) that T put into the hands of young analysts. 

 In some other varieties, the quantity of alumina was rather 

 greater than in the red stilbite. Probably its constituents are, 



1 atom bisilioate of lime, _ - - 7-5 



3 atoms bilicate of alumina, - - - 18-75 



5 atoms water, _ _ - - 5-625 



31-875 



Very fine specimens of Heulandite have lately been brought 

 to Edmburgh from the Faroe islands. They are all crystal- 

 ized, and the only shape which 1 have noticed, is that figured 



