1885.] *0 IGenth. 



[2] xxv, 198), who showed that the so-called chalcodite of C. U. Shep- 

 ard, in all probability belongs to stilpnomelane, and, if this suggestion is 

 correct, that this mineral contains both ferrous and ferric oxides, while 

 Rammelsberg (Mineralcheniie, 1875), assumes only ferrous oxide. 



From Dr. A. E. Foote, who has lately collected this mineral at the 

 Sterling Mine near Antwerp, N. Y., I have received some very pure mate- 

 rial, which made it desirable to reexamine it, especially with reference to 

 the state of the oxidation of the iron. 



For the determination of the ferrous oxide, 0.3522 grm. were dissolved 

 in dilute sulphuric acid, after the air had been driven out by carbonic 

 dioxide ; and the ferrous oxide determined by titration with potassium 

 permanganate ; the water was determined directly in a chloride of calcium 

 tube from 0.3635 grm. and 0.9854 grm. taken for the other determinations. 

 The analysis gave : 



Atomic ratio. 



10.2 



} = 



0.073 = 



} = 0.558 = 7.6 



= 7. 



99.09 



The empirical formula: (FeaMgi) 8 (FeAl) 2 Sii O 31 -f- 6H 2 agrees 

 closely with the above results. 



Ankerite. — Associated with the stilpnomelane is ankerite in groups of 

 curved rhombohedral crystals of a yellowish-white color. 



The analysis gave : 



CaC0 3 

 MnCO s 

 FeC0 3 

 MgCO a 



16. 



A peculiar variety of calamine, which closely resembles hydrozincite, 

 occurs as an incrustation upon a ferruginous calamine, the principal ore, 

 at the Bertha Mine, Pulaski county, Va. 



It is earthy and cryptocrystalline and some of the incrustations had a 

 thickness of 5 mm . 



I observed that after ignition it was dissolved by dilute hydrochloric 

 acid almost instantaneously, far more readily than the hydrous mineral. 



