PHYSIOGRAPHY. 275 



White Lead-Ore. 



(H.) M on Z=121 28'. (H.) (quadrihexagonal. H.) 

 Fig. 476. The same, with the addition of the replacement 

 of the obtuse angles by two planes, t on f' = 107 6'. (do- 

 decaedre. H.) Fig. 477. A combination of fig. 475 and 

 fig. 476. M on t = 143 33'. (H.) (trihexoedre. H.) 

 Fig. 478. / on s= 109 29'. (H.) (sexduodccimal H.) 

 Fig. 479. P on * = 126 27'. (H.) P on w=125 16'. 

 (H.) Poriff = 11620'. (H.) P on z=109 29'. (H.) 

 (octovigesimal. H.) 



Cleavage, parallel with M and h often perfect, generally 

 interrupted by conchoidal fracture. Fracture conchoidal. 

 Surface, M and h almost always much streaked vertically, 

 and several of the pyramidal faces horizontally. 



Lustre adamantine, passing into resinous. The former 

 is often metallic if the colors be dark. Very thin crystals, 

 and columnar compositions of them, often possess pearly- 

 lustre. Color white, prevalent, passing into yellowish grey, 

 ash-grey, and smoke-grey, or even into greyish black. 

 Sometimes, tinged green or blue by several of the salts of 

 copper. Streak white. Transparent . . . translucent. 



Rather brittle. Hardness = 3-0... 3-5. Sp. gr. = 

 6*465, of a white translucent variety. 



Compound Varieties. Twin-crystals ; axis of revolu- 

 tion perpendicular, face of composition parallal to one of 

 the faces of M. The composition is often repeated, not 

 only in parallel laminae, as in Arragonite, but likewise par- 

 allel to both the faces of M. The individuals are generally 

 continued beyond the face of composition. Thus are 

 formed the star-like crystals represented in the annexed 



