530 MINERALOGY 



found on the walls of cavities in the lead mines of Cornwall, Eng- 

 land. Crystals elongated parallel to a are associated with the iron 

 mines of West Cumberland, England, in cavities of dolomite. 



Wonderfully developed tabular crystals, associated with and 

 penetrated by acicular crystals of stibnite, are characteristic of 

 Felsobanya, Hungary. Barite has also been observed as the ce- 

 menting material in some sandstones, where also it must have been 

 deposited by double decomposition. It occurs around some springs 

 as a sinter and is also deposited in pipes in mines, being precipi- 

 tated from the mine waters. It is associated with limestones as 

 lenticular deposits, and it is from such occurrences that all the 

 commercial barite is mined. In the United States barite is mined 

 in the lead regions of Missouri, also in Tennessee, Virginia, and 

 North Carolina ; while in small amounts it is widely distributed. 

 Good crystals are found at Sterling, Colorado ; at Cheshire, Con- 

 necticut ; at the Perkiomen lead mine, Pennsylvania. 



Uses. Ground barite when pure white is used as a paint, as a 

 filler for paper, and, owing to its insolubility, in rubber goods. It 

 is also the principal source of the barium salts. The banded 

 varieties are cut and polished as vases, mantles, and for other 

 ornamental purposes. 



CELESTITE 



Celestite. Strontium sulphate, SrSO 4 ; SrO = 56.4, SO 3 = 

 43.6 ; Orthorhombic ; Type, Didigonal Equatorial ; fi : b : c = 

 .7789 : 1 : 1.2800 ; 100 A 110 = 37 55'; 001 A 101 = 58 40'; 001 A 

 Oil = 52; 102 A 102 = 78 49'; 001 A 111 = 64 21'; Common 

 forms, a (100), b (010), c(001), m(110), o (102), p(011), z (111) ; 

 Cleavage, basal and prismatic perfect, b less so ; Brittle ; Fracture, 

 uneven; H. = 3-3.5; G. = 3.95-4; Color, faint bluish white, 

 rarely red ; Streak, white ; Luster, vitreous ; Transparent to 

 translucent; a = 1.622; p = 1.623; -y = 1.629; -y - a = .007; 

 Optically ( + ) ; Axial plane = 010; Bx a = a; 2E = 88 38'. 



B.B. Often decrepitates, whitens, and fuses at 3, yielding a 

 deep red flame ; after ignition reacts alkaline with turmeric paper. 

 Fused with soda and a little coal dust in R. F. yields a sulphur 

 reaction on silver. Insoluble in acids. 



General description. In crystalline habit and general appear- 

 ance like barite, with which it is isomorphous. It is not as common 

 in its occurrence as barite and is less often associated with ore de- 





