ORDER II. BHOMBOHEJDBAL LEAD-BARYTE. 135 



yellow ; aurora-red, hyacinth-red ; hair-brown, 

 clove-brown ; pearl-grey and ash-grey. Streak 

 white, sometimes inclining to yellow. Semi- 

 transparent... translucent on the edges. 

 Brittle. Hardness = 3-5 . . . 4-0. Sp. Gr. = 7'098, 

 of a green variety from Zschopau. 



Compound Varieties. Globular, reniform, bo- 

 tryoidal, fruticose shapes: composition columnar; 

 faces of composition rough, irregularly streaked, 

 seldom smooth. Massive : composition columnar, 

 or granular ; the latter in most cases strongly 

 coherent. 



OBSERVATIONS. 



1. The preceding general description refers to the va- 

 rieties in which phosphate of lead has been found to form 

 the greatest proportion in the constituent parts. The 

 angles were measured in minute splendent crystals, of a 

 green colour from Brisgaw, a variety of which the specific 

 gravity is given = 6-9111 by HAUY. The variety from 

 Johanngeorgenstadt in Saxony, which consists of arseniate 

 of lead, yielded by measurement the lateral edge of the py- 

 ramid P = 79 40', from which the terminal edge follows 

 = 142 3 39', and a == ^4-696. It seems therefore that it 

 will be necessary in future to consider it as a particular 

 species, different from rhombohedral Lead-baryte. The 

 crystalline varieties are much the same in both these sub- 

 stances ; thus P. P +.os, (Fig. 117.)> and R . P. 

 2 (R). R + CD. P + os have been found at Johanngeor- 

 genstadt. The faces 2(R) are uneven, and P + 1, and 

 particularly P + os, which occur in the same variety, are 

 rough. Twin crystals have been found joined in a face 

 perpendicular to one of the terminal edges of P. The 

 specific gravity is = 7'208. 



