18 



The transparency varies, from translucent, through trans- 

 lucent at the edges, to opaque. 

 Is semihard, bordering upon hard. 

 Brittle. 



Gives a greyish white streak. 

 Is easily frangible. 

 Not particularly heavy, approaching the heavy (3,500). 



OBSERVATIONS. 



The lateral planes meet alternately under angles of 135* 

 and 45. From the foregoing fossil it is sufficiently dis- 

 tinguished by crystallization, fracture, inferior hardness, and 

 specific gravity. From grenatite it may readily be dis- 

 criminated, by the difference in crystallization, fracture, 

 and sort of lustre. 



CHEMICAL CHARACTERS. 



Before the blow-pipe it suffers no change, nor in the 

 heat of a porcelain furnace, when exposed in an earthen 

 crucible; but in a crucible of charcoal it melts to an 

 imperfect black glass, owing to the partial reduction of the 

 metallic contents. With considerable difficulty, and only 

 by repeated digestion, marine acid dissolves a third part 

 of the weight of this fossil, consisting partly of the menac 

 contents. Klaproth, from whom these characters are taken, 

 found it to consist of nearly equal parts menac-calx, 

 silex, and lime, to which Vauquelin joins a large portion 

 of iron calx. 



GEOGNOSTIC 



