t220 Dr. R. D. Thomsons [March 



which corresponds with 4 atoms Silica 



1 ,, Lime 

 1 ,, Alumina 

 1 ,, Water. 



Hence, its formula is C S + /S + Al S 2 + Aq. 



Article V. 

 Chemical Analysis of Wollastonite. By 

 Robert D. Thomson, M. D. 

 The term Wollastonite has been applied to a variety of 

 minerals. Hauy distinguished the table spar or bisilicate 

 of lime by this name. And the same title has been be- 

 stowed, it appears, on Zurlite, which is brought from the 

 Capo de Bove, near Rome, and is described by Remondini, 

 in the Memoirs of the Academy of Naples. 



The Wollastonite of the Castle Hill, Edinburgh, turned 

 out on analysis to be Prehnite. The other localities where 

 table spar is said to occur, must therefore, be considered 

 as doubtful. It would seem proper that the names by 

 which these minerals have been recognized, should con- 

 tinue to be attached to them, and that the name of Wol- 

 laston should be conferred on a distinct species. " I have 

 been induced," says Pr. Thomas Thomson, " in order to 

 commemorate the many obligations which mineralogy owes 

 to Dr. Wollaston, to apply the term Wollastonite, to a 

 mineral which I believe to be new, and which has a very 

 close relation to the species, which Hauy designated by 

 that name," (Edinb. Trans. 1831.) 



The following particulars were ascertained with the 

 assistance of Professor Thomson : — 



The mineral occurs in veins, in a green stone which is 

 brought to Glasgow from Kilsyth, and is found abundantly 

 on the banks of the Forth and Clyde canal. 



It possesses a white colour with a slight shade of green. 

 Texture fibrous, the fibres being arranged in tufts diverg- 

 ing from a centre, and thus having the appearance of im- 

 perfect crystallization. The edges are translucent, and the 

 lustre inclines to silky. Fracture splintery, and the frag- 

 ments are sharp edged. Hardness intermediate, between 

 that of selenite and calcareous spar; sp. gr. from 2*850 to 

 2*8760. Before the blow-pipe it melts with some difficulty 



