ORDER II. HEMI-PRISMATIC LEAD-BARYTE. 139 



p 



that line, often very considerably ; - sometimes 



9S 



faintly streaked parallel to the edges of combina- 



Pr 4- 2 

 tion with P -f- x ; generally curved. 



The faces are almost always smooth and shining. 



Lustre adamantine. Colour, various shades of hy- 

 acinth red. Streak orange-yellow. Translucent, 

 sometimes only on the edges. 



Sectile. Hardness = 2-5 ... 3-0. Sp. Gr. = 6-004. 



Compound Varieties. Massive : composition im- 

 perfect columnar or granular. 



OBSERVATIONS. 



1. According to PFAFF, the hemi-prismatic Lead-baryta 

 consists of 



Oxide of Lead 68-00. 

 Chromic Acid 32-00. 



Its chemical formula is Pb Ch, agreeing with 68-15 of 

 oxide of lead, and 31-85 of chromic acid. Before the blow- 

 pipe it becomes black and decrepitates if quickly heated ; 

 it may be melted, however, into a shining slag, containing 

 globules of metallic lead. It colours glass of borax green, 

 is soluble without effervescence in nitric acid, and pro- 

 duces a yellow solution. 



2. It has been found particularly in Siberia, where it oc- 

 curs in the neighbourhood of Beresof, in narrow veins, 

 traversing a rock, the true nature of which is not yet 

 known, accompanied by hexahedral crystals of Iron-pyrites, 

 generally in a state of decomposition, also by hexahedral 

 Lead-glance, rhombohedral and di-prismatic Lead-baryte, 

 sometimes also by hexahedral Gold. In Brazil it is met 

 with in sandstone, probably under similar circumstances. 



