SALTS OF BAR VTA. 109 



metals* In this way it occurs at Cheshire, Conn. ; Hat- 

 held, Mass. ; Rossie and Hammond, New York ; Perkio- 

 men, Pennsylvania, and the lead mines of the west. A 

 Scoharie and Pillar Point, near Sackett's harbor, are other 

 localities. Also near Fredericksburg and elsewhere, Vir- 

 ginia. The variety from Pillar Point receives a fine polish 

 and looks like marble, the colors being in bands or clouds. 



Uses. Heavy spar is ground up and used as white paint, 

 and in adulterating white lead. When white lead is mixed 

 in equal parts with sulphate of barytes it is sometimes called 

 Venice white, and another quality with twice its weight of 

 barytes is called Hamburgh white, and another, one-third 

 white lead, is called Dutch white. When the barytes is very 

 white, a proportion of it gives greater opacity to the color, 

 and protects the lead from be'ing speedily blackened by sul- 

 phureous vapors ; and these mixtures are therefore preferred 

 for certain kinds of painting. There are establishments for 

 grinding barytes near New Haven, Ct., where the spar from 

 Cheshire, Ct., Hatfield, Mass., and Virginia, is used. The 

 'ron ore or ferruginous clay usually mixed with it, is separated 

 by digestion in large vats of dilute sulphuric acid. 



witherite. — Carbonate of Baryta. 



Trimetric. In modified rhombic prisms, (fig. 8, p. 26.) 

 M : M = 118° 30'; M : e = 149° 15'. Also in six-sided 

 prisms terminated with pyramids. Cleavage imper- 

 ^ct. Also in globular or botryoidal forms: often 

 massive, and either fibrous or granular. The mas- 

 sive varieties have usually a yellowish or grayish 

 white color, with 3, luster a little resinous, and are 



translucent. The crystals are often white and nearly trans 

 parent. H = 3— 3-75. Gr = 4-29— 4*35. Brittle. 



Composition : baryta 77*6, carbonic acid 22*4. Decrep- 

 itates before the blowpipe and fuses easily to a translucent 

 globule, opaque on cooling. Effervesces in nitric acid. 



Dif. Distinguished by its specific gravity and fusibility 

 from calcareous spar and arragonite ; 1 y its action with 

 acids from allied minerals that are not carbonates ; by yield- 

 ing no metal from white lead ore, and by not tinging the 

 flame red, from strontianite. 



What are the uses of heavy spar? How is witherite distinguished 

 Irom other minerals? 



10 



