CARBONATES 391 



r (1011), e (Ill2); Cleavage, rhombohedral perfect; Brittle, 

 frarture uneven; H. =3.5-4.5; G. = 3.45-3.60; Color, various 



shades of n-d or pink, yellowish gray, l>ro\vn when oxidized : Streak. 

 white; Transparent to opaque; = 1.597; Optically ( ). 



B.B. Blackens and decrepitates, infusible; with the fluxes 

 ivart- for manganese. Dissolves in hot dilute HC1 with effer- 

 QCe, yielding carbon dioxide. 



General description. Crystals are not common, but in habit 

 are simple rhombohedrons ; other forms are rare. Complex 

 warped rhombohedrons of a beautiful pink color occur in Saguache 

 County, also dark rose-colored transparent rhombohedrons asso- 

 ciated with cubes of pyrite at Alicante, Lake County, Colorado. 

 At Butte, Montana, the simple rhombohedrons are coated with 

 quartz. Fine specimens are obtained from Franklin Furnace, 

 New Jersey, where large masses of cleavable calcite occur, colored 

 pink with manganese carbonate which has crystallized with it as an 

 isomorphous mixture. 



These mixtures of calcium and manganese carbonates are given 

 definite names when the amount of manganese reaches a consider- 

 aMe percentage, as manganocalcite for the 25 per cent, mixture, 

 or manganosiderite when much iron is present. 



Rhodochrosite is formed under the same conditions as the other 

 rhombohedral carbonates, as it is more stable than the ferrous car- 

 bonate ; when they are contained in the same solution, the iron is 

 deposited first, and the manganese may be carried in solution much 

 farther from the original source. Owing to this difference of 

 stability in solution the two are almost always deposited apart. 



Artificial. Microscopic rhombohedrons may be formed by 

 he;iting a solution of manganese chloride and sodium carbonate in 

 a closed tube to 160 C. 



SMITHSONITE 



Smithsonite. Dry bone, Carbonate of zinc, ZnCO 3 ; ZnO = 

 64.8, CO = 35.2; Hexagonal; Type, Dihexagon&l Alternating; 

 c = .8063 ; 0001 A 1011 ==_42 57' 20" ; r A r' = 72 20' ; Forms, 

 r (1011), e (0112), v (2131); Cleavage, rhombohedral perfect; 

 Brittle, fracture, uneven; H. = 5 ; G. = 4.3-4.45; Color, white, 

 yellow, green, brown ; Streak, white or pale ; Luster, vitreous to 

 dull; Transparent to opaque ; = 1.618; Optically ( ). 



