OF ARTS AND SCIENCES. 451 



XVIII. 

 MELANOSIDERITE: 



A NEW MINERAL SPECIES, FROM MINERAL HILL, DELAWARE 



COUNTY, PENNSYLVANIA. 



By Josiaii P. Cooke, Jr. 

 Read, May 11, 1875. 



For the specimens of this mineral I am indebted to Mr. W. "W. 

 Jefferis, of West Chester, Pa., who informs me that the locaUty is not 

 over 500 yards from the Ilallite locality (see these Proceedings, Vol. 

 IX., page 59), lying a little off from the serpentine range in a bed of 

 clay. 



The mineral is compact and amorphous. It is very brittle, and its 

 fracture is conchoidal. Hardness about 4i-. Sp. Gr., in two determina- 

 tions (made with alcohol, but referred to water), was 3.390 and 3.392. 

 Lustre, vitreous inclining to resinous. Color, black, with a tinge of 

 red. Streak, brownish red to brick red. Subtranslucent ; and, in thin 

 plates, cherry red l)y transmitted light. Heated before the blowpipe 

 in a closed tube, it decrepitates and gives off water. In the forceps it 

 fuses at about 4^ to an iron-gray mass, which is strongly attracted by 

 the magnet. On platinum wire with soda, it dissolves with efferves- 

 cence. With borax glass it gives the reactions for iron. The powder 

 dissolves very readily in muriatic acid ; but, as soon as the amount 

 added exceeds a certain limit, the solution gelatinizes. 



In the following analysis, the water was determined by ignition ; the 

 iron and alumina were weighed together, and the amount of iron in the 

 ignited precipitate determined by titration. The silica was separated 

 and weighed in the usual way. 



