OHDER ii. PYRAMIDAL SCHEELIUM-B A RYTE. 115 



Compound Varieties. Twin crystals. Axis of 

 revolution perpendicular, face of composition paral- 

 lel to one of the faces of P -f- oo ; the individuals 

 are continued beyond the face of composition. The 

 best means of recognising this composition consists 

 in the disposition of the above-mentioned striae 

 upon the faces of P, which abruptly assume ano- 

 ther direction upon faces, that seem to belong to 

 one individual. Reniform shapes : surface drusy, 

 composition columnar. Massive : composition gra- 

 nular, faces of composition sometimes irregularly 

 streaked. 



OBSERVATIONS. 



1. Pyramidal Scheeliuni-baryte, as yet the only species 

 of this genus, consists, according to BEBZELIUS, of 



Lime 19-40. 



Oxide of Scheelium 80-42. 



The chemical formula is Ca \V 2 , which gives 19-10 of lime 

 and 80-90 of oxide of scheelium. Alone upon charcoal it 

 is infusible before the blowpipe, except that the thinnest 

 edges are converted in a very strong heat into a semi- 

 transparent vitrified mass. It gives a white glass with bo- 

 rax, the transparency of which is proportioned to the quan- 

 tity of the salt employed. 



2. More generally this species occurs in the repositories 

 of pyramidal Tin-ore, both beds and veins, accompanied 

 chiefly with prismatic Scheelium-ore, prismatic Topaz, 

 rhombohedral Quartz, octahedral Fluor-haloide, and cer- 

 tain species of Talc-mica, sometimes with octahedral and 

 prismatic Iron-ore. It is met with besides in beds con- 

 taining gold, in primitive mountains, along with rhombo- 

 hedral Quartz. A third mode of its occurrence in nature 

 is in lead-veins traversing grey wacke, where it is associated 

 with prismatic Scheelium-ore, brachytypous Parachrose* 

 baryte, and other species. 



