LIME. 



237 



St. Lawrence County. Coralloidal arragonite is credited by Dr. Emmons to the Parish 

 iron ore bed in the town of Rossie. Although this situation is favourable to the occurrence 

 of this mineral, all the specimens which I have seen, and they are quite numerous, belong to 

 the preceding species. 



GYPSUM. 



[Gypst is said to have been the ancient name of calcined sulphate of lime.] 



Chaux Sulfatec. Hauy. — Sulphate of Lime. Cleaveland. — Hydrous Sulphate of Lime. Thomson. — Prisma- 

 toidal Gypsum, or Common G3rpsum. Jameson. — Prismatoidisches Gyps-Haloid. Moks. — Gypse. Beudant. 

 — Gypsum. PhiUips, Shepard and Dana. 



^■s- 102. Description. Colour snow-white when pure, but it is often 



also yellow, red, blue, grey, green, brown and even black. It 

 occurs regularly crystallized ; also foliated, fibrous, granular 

 and compact. The primary f6rm is a right oblique angled 

 prism. Fig. 102. M on T 113° 8'. Cleavage highly perfect 

 parallel with P, imperfect parallel with M and T. Fracture 

 splintery. Lustre of the lateral faces of the prism, vitreous ; 

 that of the base, pearly. Varies from transparent to translucent on the edges. Hardness from 

 1 .5 to 2.0 ; may be scratched by the nail. Specific gravity from 2.20 to 2.40. Before the 

 blowpipe it exfoliates and melts, but with difiiculty, into a white enamel. At a lower heat, 

 the water which it contains is driven off, and it becomes friable. If then reduced to powder 

 and mixed with water, the powder becomes warm, and soon hardens into a solid mass. 



This mineral may be distinguished by its inferior hardness, and by its not effervescing in 

 acids, from the carbonate of lime, which it sometimes closely resembles. The powder of 

 fluor spar is decomposed by sulphuric acid, with the evolution of the hydrofluoric acid. 



Varieties. The transparent and highly crystallized varieties are called Selenite ; those 

 disposed in fibrous concretions. Fibrous Gypsum ; those which have a splintery fracture, 

 Compact Gypsum or Alabaster. Some varieties, composed of fine scaly or dusty and shghtly 

 cohering particles, are named Earthy Gypsum, a term which is also applied to the impure 

 kinds used in agriculture. 



Composition. Sulphuric acid 46.00, lime 33.00, water 21.00. Formula CaO.S03+2Aq. 



localities. 



In a former part of this work (page 62), I have noticed in detail the most important loca- 

 lities of this mineral, with reference to its use in agriculture and the arts. I shall therefore 

 only introduce here those notices which are interesting in a mineralogical point of view. 



Albany County. Specimens of snowy gypsum have been found in the Helderberg moun- 

 tains ; and in the town of Coeymans, it occurs in an alluvial bed twenty or thirty feet in thick- 

 ness, forming efflorescences on the sides of excavations made for roads, etc. 



