316 MINERALOGY 



General Description. Crystalline habit, occurrence, and asso- 

 ciation like smaltite, often coated with the green nickel arsenate, 

 annabergite, Ni 2 (AsO 4 )3, an oxidation product. 



Rammelsbergite is an orthorhombic form of NiAs 2 occurring very 

 sparingly at Schneeberg, Saxony. 



COBALTITE 



Cobaltite. Sulpharsenite of cobalt, CoAsS ; Co = 35.5, 

 As = 45.2, S = 19.3 ; Isometric ; Type, Tesseral Central ; Common 

 forms, c (100), o (111), e (120) ; Cleavage, cubic ; Brittle, fracture 

 uneven ; H. = 5.5-6 ; G. = 6-6.3 ; Color, reddish to silver-white ; 

 Streak, grayish black ; Luster, metallic. 



B.B. Fuses easily on coal to a magnetic globule and yields an 

 arsenic odor and sulphur dioxide fumes. Well roasted and treated 

 with borax yields a cobalt reaction. Soluble in hot nitric acid, 

 which after diluting yields a white precipitate with BaCl 2 (BaS0 4 ) . 



General description. Crystals are cubes and pyritohedrons, or 

 combinations of these two forms. In habit very much like pyrite, 

 with similar striations on the crystal faces ; crystals are much more 

 common than those of the two preceding species ; often massive, 

 granular, and disseminated. Occurs under similar conditions and 

 associations as smaltite. 



Gersdorffite, sulpharsenide of nickel, NiAsS, is similar in 

 habit, occurrence, and association to cobaltite, with which it is 

 isomorphous. 



ULLMANNITE 



Ullmannite. Sulph-antimonite of nickel, NiSbS ; Ni = 27.8, 

 Sb = 57.0, S = 15.2; Isometric; Type, Tesseral Polar; Forms, 

 a (100), e (120), d (110), o (111) ; Twins, interpenetrating tetra- 

 hedrons ; Cleavage, cubic perfect ; Brittle, fracture uneven ; H. = 

 5-5.5 ; G. = 6.2-6.7 ; Color, steel-gray to silver-white ; Streak, 

 grayish black; Luster, metallic. 



B.B. On coal in R. F. fuses easily to a globule, boils, and yields 

 an antimony coat. After roasting yields a nickel reaction with the 

 fluxes. Decomposed with hot nitric acid with the separation of 

 sulphur and white oxide of antimony. It may contain some ar- 

 senic. 



