132 MINERALS AND GEOLOGY 



crystal-faces exhibiting a vitreous or pearly- vitreous lustre.. Granu- 

 lar and rock varieties have mostly a dull earthy aspect. H =. 1.0 

 2.0; sp. gr. 2.25 2.35. Sectile, and, in thin lamellae, somewhat 

 flexible. Becomes opaque when held at the edge of a lamp or candle- 

 flame. BB, exfoliates, and melts into a white caustic enamel. In 

 the bulb-tube yields a large amount of water. Soluble in hydro- 

 chloric acid. Dissolves also, if in fine powder, in a large amount of 

 water, and more readily in a solution of rock salt. Normal composi- 

 tion : sulphuric acid 46.51, lime 32.56, water 20.93. The transpar- 

 ent crystals aud cleavable varieties are commonly termed selenite ; 

 and the fibrous and fine granular varieties form the alabaster and 

 satin spar of lapidaries, but these names are also bestowed on similar 

 varieties of carbonate of lime. When deprived of its water by ex- 

 posure to a low red heat, gypsum is converted into plaster or Plaster 

 of Paris. 



Crystalline and fibrous masses, and occasionally distinct crystals of 

 gypsum, associated with crystals of quartz, dolomite, &c., occur in 

 cavities of many of the Silurian strata in Canada, and thin bands are 

 interstratified in places with the shales and limestones of some of 

 these formations. Gypsum occurs under these conditions in the 

 Calciferous formation of Beauharnois, the Hudson River formation 

 of Point Rich on Georgian Bay, the Medina formation of St. Vincent, 

 and in the Clinton and Niagara strata in the vicinity of the Falls, 

 Hamilton, Dundas, and elsewhere. 



Rock masses of granular and compact gypsum, more or less mixed 

 with carbonate of lime, characterize the Onondaga Formation of 

 Western Canada, and occur largely in the valley of the Grand River : 

 more especially in the townships of Dumfries, Brantford, Oneida, 

 Seneca, and Cayuga ; as well as throughout the tract of country, 

 generally, between the eastern extremity of Lake Erie and the mouth 

 of the Saugeen. (See under the Onondaga Formation, in Part Y.) 

 The greater part of the gypsum from these localities is ground for 

 agricultural use. 



100. Epsomite (Epsom Salt) :. White or greyish. Soluble: taste, 

 strongly bitter. Rhombic in crystallization, but occurring chiefly in 

 fibrous tufts and earthy or botryoidal incrusting masses. H = 2.0, 

 or less. BB, runs at first into liquid fusion, and then forms an 

 alkaline infusible crust which assumes a flesh-red colour if moistened 



