370 



C— GYPSUM. ALABASTER. 



This can scarcely be considered a building-stone, and it is used only 

 to a small extent for ornamental purposes. We may, however, devote 

 a little space to the subject. 



(1) COMPOSITION AND USES OF GYPSUM. 



Pure gypsum is composed of the sulphate of lime and water in the 

 proportions of about 79.1 per cent, of the former to 20.9 percent, of the 

 latter (ante, p. 370). Three varieties are common : (1) crystallized gyp- 

 sum or selenite, which occurs in broad, flat, transparent plates sometimes 

 a yard in diameter and of value only as mineral specimens and for 

 optical purposes ; (2) fibrous gypsum, which includes the variety satin 

 spar used for making small ornaments ; and (3) massive gypsum, which 

 includes the common white and clouded varieties used in making plaster, 

 and the pure, white, fine-grained variety alabaster.* 



(2) LOCALITIES OF GYPSUM IN THE UNITED STATES. 



The principal localities of gypsum in the United States as given by 

 Danat are in New York, Ohio, Illinois, Iowa, Virginia, Tennessee, and 

 Arkansas, where it occurs in extensive beds and usually associated with 

 salt springs. It is also found associated with Triassic deposits in the 

 Pocky Mountain region. Handsome selenite and snowy gypsum are 

 also stated to occur near Lockport and Camillas, N. Y., in Davidson 

 County, Tenn, and in the form of rosettes in the Mammoth Cave of 

 Kentucky. 



According to G. F. Kunz f the ornaments of satin spar sold at Niag- 

 ara Falls and other " tourist places" are nearly all imported from Wales, 

 though some few of the common white variety are cut from the beds of 

 this stone found in the vicinity. The Italian alabaster is used exten- 

 sively in making statuettes (see p. 473), but the common varieties found 

 in this country and Nova Scotia are used chiefly for land plaster and as 

 plaster of pans, or stucco. So far as the Curator is aware the gypsum 

 quarried at Fort Podge, Iowa, is the only one that has been at all used 

 for structural purposes in this country. 



According to Dr. White § several residences, a railway station, and 

 ether minor structures, including a large culvert, have been built of 

 gypsum at this place. In the construction of the culvert the lower 

 courses that came in contact with the water were of limestone, as the 

 gypsum had proven slightly soluble and hence less durable in such po- 

 sitions. The stone is regarded by Dr. White as very durable in ordi- 



* Much of the material popularly called alabaster is in reality travertine (see p. 375.) 



t Text hook of Mineralogy, p. 393. 



t Min. Resources of the United States, 1883-'84, p. 77, 



$Geol, of Iowa, Vol. n, p. 302, 



