tiYl'SUM. 113 



H = l*5 — 2, or so soft as to be easily cut with a knife. 

 Gr = 2*31 — 2*33. The plates bend in one direction and are 

 brittle in another. 



Composition : lime 326, sulphuric acid 46*5, water 209. 

 Before the blowpipe it becomes instantly white and opaque 

 and exfoliates, and then falls to powder or crumbles easily in 

 the fingers. At a high heat it fuses with difficulty. No 

 action with acids. 



The principal varieties are as follows : 



Sclenite, including the transparent foliated gypsum, so 

 called in allusion to its color and luster from sdene, the Greek 

 word for moon. 



Radiated gypsum, having a radiated structure. 



Fibrous gypsum or satin spar, white and delicately fibrous. 



Snowy gypsum and alabaster, including the white or light- 

 colored compact gypsum having a very fine grain. 



Dif. The foliated gypsum resembles some varieties of 

 Heulandite, stilbite, talc and mica ; and the fibrous, looks like 

 fibrous carbonate of lime, asbestus and some of the fibrous 

 zeolites ; but gypsum in all its varieties is readily distin- 

 guished by its softness ; its becoming an opaque white powder 

 immediately and without fusion before the blowpipe, and by 

 not effervescing nor gelatinizing with acids. 



Obs. New York, near Lockport, affords beautiful selenite 

 and snowy gypsum in limestone. At Camillus and Manlius, 

 N. Y., and in Davidson county, Tenn., are other localities. 

 Fine crystals of the form represented in figure 1, come from 

 Poland and Camfield, Ohio, and large groups of crystals fronj 

 the St. Marys in Maryland. Troy, N. Y., also affords crys. 

 tals in clay. In the mammoth cave, Kentucky, alabaster 

 occurs in singularly beautiful imitation of flowers, leaves, 

 shrubbery and vines. Alabaster comes mostly from Caste - 

 lino in Italy, 35 miles from Leghorn. Massive gypsum oc- 

 curs abundantly in New York, from Syracuse westward to 

 the western extremity of Genesee county, accompanying the 

 rocks which afford the brine springs ; also in Ohio, Illinois, 

 Virginia, Tennessee, Arkansas and Nova Scotia. It is 

 abundant also in Europe. 



Uses. Gypsum \vhen burnt and ground up forms a white 



What is the composition of gypsum 1 What js alabaster? What 

 effect is produced by heat ? How is gypsum distinguished from talc, 

 wiica anti other minerals ? 



10* 



