126 



NEW YORK STATE MUSEUM 



dated with sulfur and other eruptive minerals. Beautiful crys- 

 tals have been obtained from Girgenti, Sicily. It also occurs 

 at several localities on Lake Erie; at Lockport, Ohaumont bay. 

 Rossie and Schoharie N. Y. : in Pennsylvania, West Virginia. 

 Tennessee, Kansas, Texas and California, and at Kingston 

 Canada. 



As a source of strontium nitrate, celestite is much used in the 

 manufacture of fireworks. 



Crocoite PbCr0 4 

 Crocoite is a lead chromate occurring in monoclinic crystals 

 of prismatic habit and in imperfectly columnar and granular 

 masses. It is of a bright hyacinth-red to orange-yellow color. 

 The luster is adamantine. 



Brochantite 4CuO.S0...3H 2 

 Brochantite is a basic sulfate of copper commonly found in 

 acicular orthorhombic crystals or drusy crusts of an emerald 

 green or blackish green color and vitreous luster. 



Gypsum (selenite, alabaster) CaS0 4 -2IL0 



Gypsum is a hydrous calcium sulfate. 



The crystals are monoclinic and commonly quite simple in 

 form. fig. 245 and 246 representing types of common occurrence. 



Gypsum 



Twins of the arrowhead form shown in pi. 38 2 are quite fre- 

 quent. Massive forms have a foliated, lamellar or granular 

 structure and a fibrous variety known as satin spar is often of 

 marked beauty. Easy cleavage parallel to the clinopinacoid 

 yields thin polished plates. The color varies from white to 

 gray, flesh-red, yellow or light blue. The luster is pearly to sub- 

 vitreous. 



