396 MINERALOGY 



Optically ( ); Axial plane parallel to 100; Bx a = c; 2E = 

 ]036'. 



B.B. Fuses in the forceps with difficulty and yields a deep 'red 

 flame ; after ignition reacts alkaline with turmeric paper. Effer- 

 vesces in cold dilute HC1. 



General description. Crystals are often sharply pointed in 

 habit, caused by the development of the acute pyramid and brachy- 

 dome, as at Hamm in Westphalia, also columnar, fibrous, or 

 granular. 



It is isomorphous with barium and calcium carbonates and 

 usually contains some of these salts. In its occurrence it is asso- 

 ciated with galena in ore deposits, and with barite and celestite; 

 from the latter it may have been derived as a secondary product, as 

 at Mount Bonnell near Austin, Texas ; occurs also in Jefferson 

 County, New York, and in Monroe County, Michigan. 



Strontianite is the commercial source of the salts of strontium, 

 which are used to produce the red fires in pyrotechnics. The hy- 

 drate is used in the beet sugar industry to precipitate the sugar 

 from the molasses ; for this purpose barium hydrate, owing to its 

 cheapness, is sometimes used as a substitute. 



Artificially produced like witherite. 



CERUSSITE 



Cerussite. Carbonate of lead, PbC0 3 ; PbO = 83.5, CO 2 

 = 16.5 ; Orthorhombic ; Type, Didigonal Equatorial ; a : b : c 

 = .6099 : 1 : .7230 ; 100 A 110 = 31 22' 55" ; 001 A 101 = 49 

 51'; 001 A 011=35 52'; Common forms, c (001), m(110), 

 b (010), P (111) i (021) ; Twinning plane, 110; Cleavage, m and i 

 distinct ; Brittle ; Fracture, conchoidal ; H. = 3-3.5 ; G. = 6.46- 

 6.57; Color, white, yellow, or gray; Streak, white; Luster, ada- 

 mantine to resinous; Transparent to opaque; a = 1.804; |3 = 

 2.076; -y = 2.078; Optically (-); Axial plane parallel to 010; 

 Bx a = c; 2V = 8 14'; 2E = 17 8'. 



B.B. Darkens in the closed tube and decrepitates. On coal 

 in R. F. reduces to malleable lead and yields a lead coat. Dis- 

 solves in dilute nitric acid with effervescence, yielding carbon 

 dioxide. 



