< MIltu.NATKS 



Transparent to t ran.-lucent ; 0=1.740; Optically ( ); A\i:d 

 plane parallel to 010 ; Bx tt = c ; 2E = 26 30'. 



B:B. - Fuses easily to a globule and yields a green flame in the 

 forceps. After ignition reacts alkaline wit h turmeric paper. KfiVr- 

 es with cold dilute IK'l; the solution greatly diluted yields a 

 white precipitate with H 2 S04. 



General description. Witherite occurs, as a rule, not in well- 

 f on ned crystals, but in masses with a radiated, columnar, botryoi- 

 dal, or granular structure. When crystals are well developed, they 

 are pseudohexagonal in shape, from the repeated twinning parallel 

 t> 110. 



Its genesis and associations are like aragonite, but it occurs more 

 often in veins with barite and galena. By the action of waters 

 containing sulphates in solution witherite will he transformed to 

 barite. Witherite is not a common mineral, and it occurs in the 

 I'nited States in but few localities, as at Lexington, Kentucky, 

 and near Thunder Bay, Lake Superior. At Fallowfield, England, 

 it is mined commercially; splendid crystals are otained at this 

 locality. 



It is isomorphous with aragonite and alstonite or bromlite; 

 (Ba, Ca) CO 3 is such a mixture, found in pseudohexagonal crystals 

 at Alston Moore, England, while barytocalcite, BaCa (CO 3 )2, is 

 pr< 1 >ably a double salt and monoclinic in symmetry. 



Witherite is the source of barium salts ; it is used as a substitute 

 in paints, and in powder as a rat poison. 



Artificially it is formed when the carbonate is fused with sodium 

 chloride, or in the precipitation of a hot solution of barium salts 

 l>v ammonium carbonate. 



STRONTIANITE 



Strontianite. Strontium carbonate, SrCOs ; Sr = 70.1, CO 2 

 = 29.9 ; Orthorhombic ; Type, Didigonal Equatorial ; a : b : d 

 = .6090 : 1 : .7238 ; 100 A 110 =31 20' 30"; 001 A 101 = 49 

 55' 30"; 001 A Oil = 35 54'; Common forms, c (001), b(010), 

 m (110), i (021) ; Twinning plane, 110; Cleavage, prismatic good : 

 Brittle ; Fracture, uneven ; H. = 3.5-4 ; G. = 3.68-3.71 ; Luster, 

 vitreous; Color, white, yellow, gray, pale green; Streak, white; 

 Transparent to translucent; a= 1.515; p = 1.664; -y = 1.666; 



