MENACANE, AND ITS ORES. 133 



choidal, passing into the uneven. The fragments are inde- 

 terminately angular, tolerably sharp edged. The transpa-. 

 rency varies, from translucent, through translucent at the 

 edges, to opaque. Is semi-hard, bordering upon hard. 

 Brittle. Gives a greyish white streak. Is easily frangible. 

 Not particularly heavy, approacliing the heavy (3,500). ■ 



OBSERVATIONS. 



The lateral planes meet alternately under angles of 135o Observations 

 and 45. From the foregoing fossil it is sui&ciently distin- °^ '"^^^ "=• 

 guished by crystallization, fracture, inferior hardness, and 

 specific gravity. From grenatite it may readily be discrimi- 

 nated, by the difference in crystallization, fracture, and sort 

 of lustre. 



CHEMICAL CHARACTERS. 



Before the blow-pips it suffers no change, nor in the heat Chemical cha- 

 of a porcelain furnace, when exposed in an earthen cru- racters. 

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

 black glass, owing to the partial reduction of the metallic 

 contents. With considerable difdculty, and only by re- 

 peated 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 OCCURRENCE. 



In the mountains of Passau, this fossil is found inibedded Geognostic 

 in a coarse granular aggregate of felspar and hornblende, and occurrence of 

 felspar and actynolile; therefore belonging to the genus 

 green-stone, and order of primitive trap. In Norway it oc- 

 curs in rocks belonging to the same formation, in which the 

 celebrated layers of magnetic iron ore lie, and is associated 

 with hornblende, and several individuals of a tribe not as yet 

 sufficiently examined and described, but which evidently 

 constitute middle links between actynolite and hornblende, 

 and to which the names arendalite and acanticone have been 

 applied. Near Dresden and Briinn it is found dispersed 

 through sienite; and at Galway, in Ireland, in an .vqcom- 

 monly beautiful porphyritic sienite. Hence it appears, that 



th 



