SULPHATES, C'Hlii>M.\Ti:s. ITT. 531 



posits; but is more often associated with gypsum and halite 

 deposits, and fills cavities in limestones and dolomites, where it haa 

 Keen deposited liy percolating waters. Sulphur and cdr>tite an- 

 conmion associates in the region of volcanoes or solfataras. The 

 mo<t noted occurrence of this 

 character is that of Girgenti, 

 Sicily, which furnishes beautiful 

 crystals of both celestite and sul- 

 phur. At many localities, as at 

 Tyrone, Pennsylvania, a fibrous 

 blue celestite, filling veins, oc- 

 curs. A reel variety occurs in 

 Brown County, Kansas. Very 

 large crystals are found on Stron- 

 tian Island, Lake Erie. Clear 

 crystals associated with cole- Fl(j 519 ._ cvl(istit( , p ut . in . Bay , Oh io. 

 maiiite occur in Death Valley, 



California; also large crystals at Lampasas, Texas. Celestite is 

 the source of strontium salts ; for their uses see strontianite. 



ANHYDRITE 



Anhydrite. Calcium sulphate, CaSO 4 ; CaO = 41.2, SO, 

 = 58.8; Orthorhombic ; Type, Didigonal Equatorial ; a:b:c= 

 .8932: 1: 1.0008; 100 * 110 = 41 46'; 001 A 101 = 48 15'; 001 * 

 Oil == 45 1'; Common forms, a (100), b(010), c(001), m(110), 

 z(lll); Twinning plane, 012; Cleavage, basal and brachypina~ 

 choidal perfect, a less so ; Brittle ; Fracture, uneven ; H. = 3-3.5 ; 

 G. = 2.9-3; Color, white, gray, or pale shades of yellow, blue, or 

 red; Streak, white; Luster, vitreous; Transparent to translu- 

 cent; a = 1.569; p = 1.575; ? = 1.613; 7 - a = .044; Opti- 

 cally (+); Axial plane, 010; Bx a = a; 2E = 70 18'. 



B.B. Whitens and fuses at 3, yielding a yellowish red flame 

 (Ca); after ignition reacts alkaline with turmeric paper. Fused 

 with a little coal dust in R. F. on coal yields a sulphur reaction 

 with silver. Soluble in HC1. Yields no water in the closed tube. 



General description. Crystals are not common ; when well 

 formed they are stout, tabular combinations of the three pinacoids, 

 in combination with a pyramid or two, as at Aussee in Styria. A 

 simple combination of the two unit domes elongated parallel to the 



