304 MINERALOGY 



ALABANDITE 



Alabandite. MnS; Manganese sulphide; Mn = 63.1, S = 

 36.9 ; Isometric ; Type, Ditesseral Polar ; Common forms, a (100), 

 d(110),o(lll); Twinning plane, 111 ; Cleavage, cubic, perfect; 

 H. = 3.5-4 ; G. = 3.95-4.04 ; Brittle, fracture uneven ; Color, 

 iron-black ; Streak, green ; Luster, dull submetallic. 



B B On coal in O. F. yields sulphur dioxide odor ; the black 

 oxide remaining reacts for manganese with the fluxes. Soluble 

 in dilute hot HC1, yielding hydrogen sulphide. 



General description. Crystals are combinations of the cube 

 and the rhombic dodecahedron, often repeatedly twinned after the 

 spinel law ; more often massive or granular. On exposure weathers 

 to a brown color. 



Alabandite is not a common sulphide, and for that reason it is 

 commercially unimportant. In the United States it occurs in the 

 Snake River region, Colorado, where it is associated in veins with 

 argentite, pyrite, galena, and rhodochrosite, also at Tombstone, 

 Arizona, in large but rough twinned cubes. 



CINNABAR 



Cinnabar. HgS ; Mercuric Sulphide ; Hg = 86.2, S = 13.8 ; 

 Hexagonal; Type, Trigonal Holoaxial; c = 1.1453; 0001 A 1011 = 

 52 54', r v r' = 8723'; Common forms, c (0001), m (1010), 

 r(1011); Twinning axis c, interpenetrating; Cleavage, m perfect; 

 H. = 2-2.5; G. = 8-8.2; Slightly sectile, fracture conchoidal; 

 Color, cochineal-red to dark red ; Streak, scarlet ; Luster, adaman- 

 tine; Transparent to opaque; o> = 2.854, = 3.201 - o> = 

 .447; Optically (+); Circular polarization. 



B.B. On coal in 0. F., when pure, volatilizes entirely, yielding 

 a sulphur dioxide odor and possibly a gray coat. Heated in the 

 closed tube with dry soda yields a sublimate of metallic mercury. 



General description. A very heavy massive reddish brown 

 mineral, at times almost black from organic matter, or earthy and 

 disseminated. Crystals are not common, but occur in rhombohe- 

 dral habit, in short thick crystals, combinations of the unit prism 

 terminated by a rhombohedron, or by the base, when the habit is 

 tabular. The most general form of the type, the trigonal trapezo- 

 hedron, is very rare, but several have been described on crystals 



