68 Dr T. THOMSON'S Account of the 



possession, seems to be almost as abundant in Strontian mine as 

 the preceding. 



Its colour is yellowish-brown. 



It is composed of needles much finer than those of the green 

 variety, and, as in it, slightly diverging from a common centre. 



Specific gravity 3.651. 



Its constituents, as determined by Mr THOMAS Mum, are, 



Carbonate of Strontian, . . 91.171 



Carbonate of Lime, . . . 8.642 



Carbonate of Manganese, . 0.099 



Oxide of Iron and Alumina, 0.078 



99.990 

 It is a compound of 



1 atom carbonate of lime, 



7 atoms carbonate of Strontian. 



16. Quatersilicate of Alumina. 



About two years ago, I received from Mexico, among a va- 

 riety of minerals, one which I set aside for a chemical exami- 

 nation. It was ticketed, " Piedran Barras ? Dipiro de HAUY ? 

 De Cymophan." It was obvious at first sight that the mineral 

 was neither the Dipyre of HAUY nor Cymophane ; nor could I 

 assign it a place in my cabinet. 



Its colour is yellowish-white. 



Its structure is radiated ; for it is composed of imperfect, ob- 

 lique four-sided prisms, diverging slightly as from a centre. The 

 surface of the prisms is striated longitudinally ; and I could dis- 

 cover no cleavage to lead to any inference respecting the pri- 

 mary form. 



