New Cobalt Minerals. 333 



analysis agrees quite exactly with mine, and leads to the same 

 formula of composition. The arsenic-pyritical one has exactly 

 the same form as the arsenic-pyrites, and is distinguished from it 

 by a reddish color resembling cobalt-glance ; points it directly 

 to the composition of arsenical-pyrites, wherein a part of the iron 

 is replaced by a quantity of cobalt varying in different individ- 

 uals. From the crystals examined by me, I found the follow- 

 ing compositions : 



Iron, ... - 30.9 



Cobalt, - - - - 4.7 



the exact mispickel lustre and crystalline form, even to the streaking of the prisms. 



Sp. Gr. = 6.23. The analysis of crystals from two to three lines in length gave 

 Sulphur, - - , - - . - - 17.57 



Arsenic, - - - - - - - 47 55 



Iron, ....... 26.54 



Cobalt, ....... 8.3] 



99.97 



It would appear moreover, that the proportion of cobalt varies with the size of 

 the crystal, — the larger the crystal, the smaller being the content of cobalt. 

 ScHEERER supposes that its presence is not attributable to a mechanical source, 

 but that it aids in forming a strictly chemical compound, inasmuch as the cobalt 

 replaces the iron. He adds some account likewise of the geological position of the 

 ore with reference to the occurrence of the cobalt mine of Skutterud. This last 

 forms a vertical bed, or stratum whose direction is north and south, and termin- 

 ates suddenly at the southern declivity of a mountain. Following the direction of 

 this stratum nearly a mile, there is found on the opposite side of the Storcte river, 

 the cobaltic-arsenical-pyrites bed, having the identical arrangement with that af- 

 fording the cobalt glance. It would hence appear that the cobaltic stratum had 

 supplied cobalt to that containing the mispickel as long as the metal held out. 



The other variety has a tin or silver lustre, and a Sp. Gr. =6.78. It occurs com- 

 pact, with a conchoidal fracture, and a more or less distinct tesseral cleavage : 

 also in single crystals exhibiting octahedral, cubic rhombo-dodecahedral and icos- 

 itetrahedral faces. According to Scheerer, it contained. 



Arsenic, -...-,. 77.84 



Cobalt, - - 20.01 



Sulphur, 0.69 



Iron, ....... 1,51 



Copper, - - - - - - -in traces. 



100.05 



BREiTHAUPThas described this ore under the name of Tesseralkies. — Poggend, 

 Ann. d. Phys. B. XLII, S. 546/. 



The first mentioned ore here described, is without doubt, the same substance 

 which was noticed at Franconia, N. H., in 1824 by Dr. J. F. Dana of Dartmouth 

 College, (Vol. viii, p. 301, this Journal,) and subsequently in 1833 by Mr. A. A. 



