ORDER II. PYRAMIDAL LEAD-BARYTE. 141 



sometimes striated parallel to the edges of com- 

 bination with P. P 3 commonly rough, -^-? 

 P 3 often, P 1 and [P + cc] always 

 rough; P + oo and [(P 4- oo) 5 ] smooth, but 

 curved, so that if they occur together in a crys- 

 tal, they are joined without producing a distinct 

 edge between them. 



Lustre resinous. Colour generally wax-yellow ; 

 passing into siskin-green and olive-green, also 

 into orange-yellow, yellowish-grey, and greyish- 

 white. Streak white. Semi-transparent, trans- 

 lucent on the edges. 



Brittle. Hardness = 3-0. Sp. Gr. = 6-760, 

 orange-yellow crystals from Annaberg in Austria. 



Compound Varieties* Massive, composition gra- 

 nular, of various sizes of individuals, and firmly 

 coherent. 



OBSERVATIONS. 



1. The pyramidal Lead-baryte, according to KLAPROTH 

 and HAT CHE TT, consists of 



Oxide of Lead 64-42 58-40. 



MolybdicAcid 34-25 38-00. 



Oxide of Iron 0-00 2-08. 



Silica 0-00 0-28. 



The chemical formula is Pb Mo 2 , which is equivalent to 

 60-86 oxide of lead, and 39-14 molybdic acid. It is with 

 difficulty and slowly soluble in acids. Before the blowpipe 

 it decrepitates briskly, and assumes a darker colour, which, 

 however, again disappears. Alone upon charcoal it melts, 

 is absorbed by it, and leaves behind some reduced globules 

 of metallic lead. 



2. The varieties of this species are found in beds and 



