108 DR BREWSTER on Hopeite, a New Mineral, 



Having determined, by many physical experiments, that it was 

 not Silicate of Zinc, I was anxious to obtain as much as would be 

 sufficient for the purposes of analysis. Mr HEULAND exerted 

 himself with his usual zeal for science, to obtain additional speci- 

 mens ; but Major PETERSEN, to whom he applied for this pur- 

 pose, informed him, that there was reason to believe that no spe- 

 cimens had been found excepting those which Mr HEULAND had 

 already received. 



As those specimens were insufficient for chemical analysis, it 

 became necessary to examine the mineral by means of other 

 methods of observation, by which its existence as a New mineral 

 species was completely established. 



Description of the Mineral. 



Physical Character. The specific gravity of a perfect crystal 

 was 2.76, and that of a larger specimen, with some black metal- 

 he particles adhering to it, was 2.91. It is scratched by calcare- 

 ous-spar, and its hardness is consequently below 3.0 of MOHS'S 

 scale. It is neither phosphorescent nor electric by heat. 



The mineral must therefore be placed beside Anhydrite and 

 Cryolite, in the 1st order, or that of Haloide of the 2d class of 

 MOHS'S System. 



Optical Character. It has two axes of double refraction, the 

 principal one of which is perpendicular to the axis of the prism, 

 and also to the planes of most eminent cleavage. The action of 

 this principal axis is negative, like that of calcareous spar ; and 

 the inclination of the resultant axes of double refraction, mea- 

 sured with as much accuracy as the specimen would permit, is 

 about 48. The index of the ordinary refraction, through one 

 of the summit planes, and one of the faces of the prism, was 

 nearly 1.601. 



