PHYSIOGRAPHY. 113 



Plumbo-Gummite. 



PLUMBO-GUMM1TE. Staphyline Lead-Baryte. 



Reniform. Surface smooth. Composition thin colum- 

 nar . . . impalpable. 



Cleavage, parallel with the sides of a rhombic prism, in 

 traces. Fracture conchoidal. 



Lustre resinous. Color yellowish-brown and reddish- 

 brown, striped. Translucent. 



Hardness =4-0 . . . 4-5. Sp. gr. =6-3 . . . 6-4. 



If rubbed in an isolated state, it acquires a strong nega- 

 tive electricity. 



1. If quickly heated before the blow-pipe, it decrepitates, and loses its 

 water; but is infusible by itself. With borax, it yields a transparent, 

 colorless glass, without reducing the lead. Its powder is decomposed 

 by concentrated muriatic acid. 



2. Analysis. 

 By BERZELIUS. 



Oxide of lead 40-14 



Alumina 37-00 



Water 18-80 



Sulphurous acid 0*20 



Lime, oxides of iron and manganese - - 1*80 



Silica 0-60 



3. It occurs at Huelgoet, near Poullaouen in Brittany, in clay-slate, 

 along with Galena, Blende, Iron Pyrites and Pyrbmorphite. 



PL.USIN-GLANCE. 



Massive ; in druses. 



Color, between iron-black and blackish lead-grey. 

 Hardness (scale of BREITHAUPT) = 3. Sp. gr. =6-189 ... 

 6-244. 

 1. It is found at Freiberg. 



POLYBASITE. Axotomous Polypoione- 



Gla n c e. 



Primary form. Regular hexagonal prism ? 

 10* 



