372 Dr. Thomas Thomson on some new [May 



the angles, even with a common goniometer. The only- 

 angle of the prisms that it was possible to try, measured 

 about 130°, shewing that the prism could not be regular. 

 Three cleavage planes were rather obscurely perceptible 

 They were parallel to the faces of an obtuse rhomboid, 

 which seemed to meet at angles of about 100° and 80°. 



Texture, foliated ; lustre, vitreous ; translucent ; hard- 

 ness about 3* ; specific gravity 4*141. 



On subjecting it to analysis I obtained 



100-00 

 From this analysis I think it probable that the mineral 

 is a compound of 



1 atom sulphate of barytes. 



2 atoms carbonate of barytes. 



Sp. 4. Calcareo- Carbonate of Barytes. — I give this name 

 to a mineral first described by Mr. Brooke, # and called by 

 him baryto-calcite. This name I could not adopt, for a 

 reason that will appear when the next following species is 

 described. 



It exists in considerable quantity at Alsten Muir, in 

 Cumberland, both crystallized and massive. 



Its colour is white, with a shade of gray, yellow, or green. 

 Cross fracture, uneven or imperfect and conchoidal. 



The primary form of the crystal is an oblique rhombic 

 prism. 



Pon M or M' 102° 54' 

 M on M' 106° 54' 



The obtuse edges of the prism are almost always replaced 

 by tangent planes. 



Lustre, vitreous, inclining to resinous ; varies from trans- 

 lucent to transparent ; hardness 4. Specific gravity, as 

 determined by Mr. Richardson in my laboratory 3*6363. 



Before the blowpipe it does not fuse per se, but melts 

 easily with borax and biphosphate of soda into a trans- 

 parent glass. 



* Annals of Philosophy, (Second Series) viii. 114. 



