PHYSIOGRAPHY. CLASSIC 



contain manganese. It occurs in reniform, botryoidal, fru- 

 ticose, and arborescent shapes, in froth-like coatings on other 

 minerals, &c., or also massive. Its composition is colum- 

 nar, generally impalpable, and often curved lamellar, the 

 fracture flat conchoidal, even, or earthy. Some varieties 

 possess imperfect metallic lustre. The colour is brown, in 

 various shades, the streak corresponding to the colour, only 

 shining. It is opake, very sectile, soils and writes ; the 

 hardness is about 0-5, specific gravity = 3706. It must 

 be observed here, that although the varieties seem to be 

 very light when lifted with the hand, yet they imbibe wa- 

 ter with violence, as soon as they have been immersed into 

 it, and they sink immediately ; from which it appears that 

 those indications of the specific gravity which state it as 

 being below I'O, must be erroneous. Black Wad mixed 

 with lint-seed oil undergoes a spontaneous combustion. Ac- 

 cording to KLAPROTH, a variety from the Hartz consists of 



Oxide of Manganese 68-00. 



Oxide of Iron 6'50. 



Water 17'50. 



Carbon 1-00. 



Baryta and Silica 9 '00. 



Brown Iron-froth is frequently found in various imitative 

 shapes in geodes of prismatic Iron-ore. Black Wad pro- 

 bably occurs under similar circumstances. Very fine va- 

 rieties of the first are met with at Huttenberg, Friesach, 

 Loben, and other places in Carinthia, also at Kamsdorf in 

 Thuringia. The localities of Black Wad are particularly 

 Devonshire and Cornwall, but also the Hartz and Pied- 

 mont. This is probably also the colouring matter in the 

 dendritic delineations upon steatite, limestone, and other 

 substances. 



