430 MINERALOGY 



at that temperature for some time; or a-CASi0 3 may be in- 

 verted to jS-CaSiOs by the addition of a fluoride or boric acid and 

 cooling slowly. 



RHODONITE 



Rhodonite. Manganese metasilicate, MnSiO 3 ; MnO == 54.1 

 SiO 2 = 45.9 ; Triclinic ; Type, Centro-symmetric ; & : b : c - 

 1.0729:1:. 6213; a = 103 18'; P = 108 44'; -y = 81 39' 

 100 A 010 = 94 26'; 100 A 001 = 72 36'; 010 A 001 = 78 42' 

 100 A l 10 = 48 33'; Crystal forms, c(001), a (100), b (010) 

 m (110), M (110) ; Cleavage, prismatic (92 28') perfect, c less so : 

 Brittle ; Fracture, uneven ; H. = 5.5-6.5 ; G. = 3.4-3.7 ; Color, 

 shades of red and pink ; Streak, white ; Luster, vitreous to pearly, 

 Translucent to opaque; Optically (-) ; 2 V = 76 12'. 



B.B. Fuses at three to a black slag. With borax yields a 

 manganese reaction. Nearly insoluble in acids ; some may effer- 

 vesce from containing carbonates, and others (fowlerite) may yield 

 a zinc coat on coal. 



General description. Crystals are usually large and rough, 

 combinations of the three pinacoids, flattened parallel to the base or 

 elongated parallel to the vertical axis. The crystal faces often 

 appear glassy, as if fused ; also massive, granular, or in rounded 

 separate grains. On exposure the surface blackens from oxidation, 

 and impure varieties may be yellow or green ; this variation in color 

 is due to the replacement of manganese by iron, calcium, or zinc. 

 Fowlerite from Franklin, New Jersey, is a light-colored form con- 

 taining as much as 7 per cent. ZnO ; while bustamite is a variety 

 containing at times as much as 20 per cent. CaO. 



Rhodonite is found in schists and metamorphic limestones ; it is a 

 product of contact metamorphism. At Franklin, New Jersey, it is 

 associated with wollastonite, spinels, and garnets. At Filipstad 

 in Sweden it is associated with the iron ores. A massive variety is 

 mined near Ekaterinberg, Urals, Russia, and used as an ornamental 

 stone. 



In weathering the manganese forms carbonates. The silica 

 forms a soluble silicate and quartz ; when the decomposition is 

 incomplete, the mineral is a mixture of silicate and carbonate. 



