1821.] Mr. Squires on Xhomsonile. 255 



the extremities. The lateral planes are longitudinally striated. 

 The crystals are imposed on the same mineral, massive, which 

 is uneven and sparry. 



The lustre is vitreous, inclining to resinous externally, inter- 

 nally splendent. The fracture is fibrous ; cross fracture small and 

 earthy ; in the massive inclining to splintery. 



It is transparent in the largest specimens, which are rare ; the 

 massive translucent on the edges. 



It scratches rhomb spar, and is scratched by fluor. It is 

 easily frangible. 



Specific gravity very low ; as near as I could calculate only 

 about 2-15. 



Under the blowpipe, it, with difficulty, fuses into a white 

 enamel. It slowly effervesces with the acids, and loses 38 per 

 cent, in weight, leaving six parts of an insoluble powder, which 

 has the properties of silicia. The solution holds lime and mag- 

 nesia, which, when separated, as correctly as I could, by Dobe- 

 reiner's method {Annals, Nov. 1818), which is to precipitate with 

 carbonate of ammonia, &c. yielded 30 parts lime, and 19 parts 

 magnesia. A few grains of salt of potash I unfortunately neg- 

 lected, which makes the analysis more imperfect than I could 

 wish. Meanwhile, it stands thus : 



Lime 30 



Magnesia 19 



Carbonic acid 38 



Silicia Q 



Potash, water, and loss 6 



100 



It occurs in a chalk pit belonging to Mr. Fountain, of this 

 city, near Little Catton. 



This mineral not being described in any system, I have ven- 

 tured to designate it Ihomsonite, in honour of the illustrious 

 ehemist and mineralogist of that name, and Professor in 

 Glasgow. 



I shall endeavour to forward you a specimen, by the hand of 

 a friend, at an early day for your examination P. S. 



