458 DR T. THOMSON'S Analysis of some Minerals. 



V. Wollastonite. 



This name was given by LEMAN to a mineral which occurs in 

 the lava of Capo di Bone, near Rome. I have never seen a spe- 

 cimen of it ; but Mr W. PHILIPS informs us, that, by mechanical 

 division, it yields a crystal precisely the same with the primary 

 form of table-spar or bisilicate of lime, of which it can scarcely be 

 said to be a variety *. But there is a mineral which occurs in 

 the rock of Edinburgh Castle, to which the Edinburgh mineralo- 

 gists have given the name of Wollastonite, probably from a no- 

 tion that it is the same with LEMAN'S mineral. I had an oppor- 

 tunity of seeing and examining some specimens of this mineral 

 last September, and was surprised to find it to be a mineral very 

 different indeed from table-spar, being in fact very pure prehnite. 

 The total want of the shade of green which usually characterizes 

 prehnite, seems to have prevented the true nature of this mineral 

 from being recognised. But abundance of prehnite, quite free 

 from every tint of green, is met with in the neighbourhood of 



Silica, ......... 48.988 



Alumina, ........ 19-774 



Soda, ......... 6.066 



Lime, ......... 4.068 



Peroxide of iron, ..... 0.404 



Water, ......... 20.700 



100. 



This approaches BERZELIUS' specimen, and shews us, that the lime in chabasite 

 may be replaced by soda. The formula is, 



* PHILIP'S Mineralogy, p. 211. 



