Eakle.] 



Mineralogical Notes. 



321 



form very similar to opal deposits. The mineral has a coal black 

 color and a bright vitreous luster, showing an occasional iridescent 

 tarnish. It is translucent on its edges, and thin splinters are 

 yellowish-red in transmitted light. The mineral is exceedingly 

 brittle, and breaks with a conchoidal fracture. It has a hardness 

 of 2.5 and a yellowish-brown streak. It is easily and completely 

 soluble in acids, but infusible, becoming magnetic after ignition. 



The average of several analyses of the black mineral showed 

 the composition: — 



Per cent. 



FeA , 56.14 



Al f O, 577 



CaO 3.35 



PA 449 



Organic 1.37 



SiO, 2.05 



H,0 at uo° C 15.94 



H 2 over 1 io° C 10.24 



99-35 



The specific gravity is 2.578. 



When the mineral was heated over a blast lamp, the ferric 

 oxide became somewhat reduced, owing probably to the presence 

 of some organic matter. As the amount of water obtained by 

 direct weighing was 26.18%, and by ignition at low red heat with- 

 out any apparent reduction was 27.55%, the difference, 1.37%, prob- 

 ably represents this organic matter. The water expelled at 1 io° C. 

 was readily reabsorbed by the pulverized mineral, and since the 

 mineral is a solid homogeneous body, all the water driven off may 

 well be considered as belonging to the composition of the mineral. 



It is impossible to state in just what condition the phosphorus 

 and other oxides exist in the substance, so, if we reckon them as 

 impurities and consider the mineral as a simple hydrous sesqui- 

 oxide of iron, the analysis reduced to 100% becomes: — 



Per cent. Ratio. 



Fe,0 3 68.20 4.61 I 



H. 2 31-80 17.66 4.14 



