THE NONMETALLIC MINERALS. 



405 



XII. SULPHATES. 

 1. BARITE; HEAVY SPAR. 



Composition BaSO^,^ Sulphur trioxide 34.3 per cent, baryta 65.7 

 per cent; specific gravity 4.3 to 4.6; hardness 2.5 to 3.5. 



Occuwence. The sulphate of barium to which the mineralogical 

 name of barite is given occurs as a rule in the form of a white, trans- 

 lucent to transparent, coarsely crystalline mineral, about as hard as 

 common calcite. but from which it may be readily distinguished by 

 its great weight and its not effervescing when treated with acid. A 

 common form of the mineral is that of an aggregate of straight or 

 somewhat curved plates, separating readily from one another when 

 struck with a hammer, and cleaving readily into rhomboidal forms 

 much like calcite. (Specimens Nos. 54988, 67372, U.S.N.M.) It is 

 also found in globular and nodular concretions (Specimen No. 66851, 

 U.S.N.M.), stalactiticand stalagmitic (Specimen No. 63778, U.S.N.M.), 

 granular, compact, and earthy masses, and in single and clustered 

 broad and stout crystals. In nature the material is rarely pure, but 

 nearly always contaminated with other elements, as noted in the 

 following analyses of samples from Fulton, Blair, and Franklin coun- 

 ties, Pennsylvania. 1 



The mineral occurs commonly in connection with metallic ores or as 

 a secondary mineral associated with sand and limestones, sometimes 

 in Distinct veins, or as in southwest Virginia, where it fills irregular 

 fractures in certain beds of the Cambrian limestone or in part replaces 

 the limestone itself . (Specimen No. 67357, U.S.N.M.). In Washing- 

 ton County, in this State, the mineral has been mined in an itinerant 

 manner by farmers on whose land it occurs, and who work mostly from 

 open cuts or trenches, rarely making an opening of sufficient size to 

 be termed a mine. As the material is less soluble in atmospheric 

 waters than is the limestone in which it occurs, it follows that often 



j * Pennsylvania Second Geological Survey, Chemical Analyses, pp. 368, 369. 



