528 MINERALOGY 



GLAUBERITE 



Glauberite. Na 2 Ca(SO 4 ) 2 ; Sodium calcium sulphate; 

 22.3, CaO = 20.1, SO 3 = 57.6; Monoclinic; Type, Digonal 

 Equatorial ; a : b : c = 1.2199 : 1 : 1.0275 ; p = 67 49' = 001 

 100; 100 A 110 = 48 29'; 001 A 101 = 30 37' ; 001 ,011 = 43 34'; 

 110,111 = 32 29'; Common forms, a (100), c(001), m (110), 

 s(lll); Cleavage, basal perfect; Fracture, conchoidal; Brittle; 

 H. = 2.5-3; G. = 2.7-2.85; Color, pale yellow, gray, or red; 

 Streak, white; Luster, vitreous; Transparent to translucent; 

 Optically (-); Axial plane J_ 010; Bx a c = 30 46' in front; 

 2E = 11. 



B.B. Whitens, decrepitates, and fuses at 1.5, coloring the flame 

 intensely yellow (Na). Dissolves in HC1; the solution yields a 

 white precipitate with barium chloride (BaSO 4 ). - Whitens in 

 water, depositing gypsum, which also dissolves in an excess. 

 Has a bitter, salty taste. 



General description. Crystals tabular in habit, combinations 

 of c, s, m, and a ; at times the pyramid predominates. The faces 

 c and s are often striated parallel to their intersection. 



Glauberite is associated with the deposits of other soluble sodium 

 salts, as at Stassfurt, Germany ; Tarapaca, Chili ; and the various 

 borax and salt lakes of Nevada and California. 



BARITE 



Barite. Heavy spar ; Barium sulphate, BaS0 4 ; BaO = 65.7, 

 S0 3 = 34.3 ; Orthorhombic ; Type, Didigonal Equatorial ; a : b : c 

 = .8152:1:1.3136; 100,110 = 39 11'; 001,101=58 11'; 

 001,011 = 52 43'; 111,001 = 64 19'; 102,102 = 77 43'; 

 Common forms, a (100), b (010), c (001), m (110), o (Oil), d (102) ; 

 Twinning planes, 110 and 601 both developed as lamellae; Cleav- 

 age, basal and prismatic perfect, b imperfect ; Fracture, uneven ; 

 Brittle ; H. = 2.5-3.5 ; G. = 4.3-4.6 ; Color, white, or pale shades 

 of yellow, green, blue, brown, or red ; Streak, white ; Luster, 

 vitreous; Transparent to translucent; a = 1.637; = 1.638; 

 y = 1.649; -y - a = .012; Optically (+); Axial plane, 010 

 Bx a = c; 2E = 63 12'. 



B.B. Often decrepitates, whitens, and fuses at 3, colorin 

 the flame yellowish green (Ba). After ignition reacts alkaline with 



