244 PHYSIOGRAPHY. 



Gypsum Haidingerite. 



crystals, several inches long, of the form of Fig. 218, are found. Near 

 Niagara falls, and at Lockport, (N.Y.) very handsome varieties of snowy 

 white, granular, and foliated Gypsum, occur imbedded in black lime- 

 stone. 



5. Gypsum is variously employed in manufacturing artificial marble, 

 stucco work, mortar, &c. ; also for making casts of statues, medals, &c. 

 It is added to the mass of certain kinds of porcelain and glass. In sculp- 

 ture, it is used under the name of alabaster. It is also employed in ag- 

 riculture, for improving the soil, both calcined, and in its natural state ; 

 it forms the paste of colored drawing pencils, and is employed in polishing. 



GUMMITE. (See Halloysite.) 

 HAIDINGERITE. Diatoraous Gypsum-Mica. 



Primary form. Right rhombic prism. M on M =99 

 52'. 



Secondary forms. The primary, having the lateral and 

 terminal angles replaced by single planes, together with the 

 truncation of the obtuse lateral edges, and the bevelment of 

 the lateral edges. The obtuse edges of the prism are 

 sometimes replaced by three pianos. 



Cleavage, highly perfect, and easily obtained in the di- 

 rection of P. 



Lustre vitreous. Color white. Streak white. Trans- 

 parent, in small crystals translucent. Double refraction ob- 

 servable through M, and the opposite face replacing the 

 obtuse edge, making an angle of 40. 



Sectile. Thin laminae, slightly flexible. 



Hardness =2-0 . . . 2-5. The face P may be scratched 

 by Common Salt. Sp. gr. = 2-48. 



1. Analysis. 

 By TURNER. 



Arseniate of lime - - - 85-681 

 Water - - - 14-319 



2. It has been observed only upon a single specimen, whose locality 

 is unknown, in the cabinet of Mr. FERGUSON, of Raith. The mineral 



