246 



DESCRIPTIVE MINERALOGY. 



Uses. This salt, which is abundantly procured as a residue of the preparation of carbonic 

 acid, etc., is employed, in consequence of its great attraction for water, to dry gases for ex- 

 perimental purposes, and to separate water from various liquids. When heated so as to 

 undergo watery fusion, there is obtained a powder which is used in the preparation of freezing 

 mi.xtures. 



DATHOLITE. 



[From the Greek, signifying turbid.] 



Chaux Boratee SUiceuse. Hauy. — Siliceous Borate of Lime. Ckovdand. — Prismatic Datolite. Jameson. — 

 Prismatisclier Distom Spatli. Mohs. — Borosilicate of Lime. Thmnson. — Datholite. Bcudant, Shepard and 

 Dana. — (It includes Esmarkite, Humboltite and Botryolite. Thomson, however, describes the latter as a 

 distinct species.) 



Fig. 119. Description. Colour greyish or greenish 



Fig. 120. white, rarely red and yellow. It occurs 



regularly crystallized and massive. The 

 primary form is a right rhombic prism. Fig. 

 119. M on M' 103° 40' {Phillips). Fig. 

 120 is one of the secondary forms. Cleavage 

 -'yJ J obtained with difficulty. Fracture uneven, 

 conchoidal. Lustre resinous or pearly. From 

 transparent to opaque. Hardness from 5.0 

 to 5.5. Specific gravity from 2.90 to 3.00. When exposed to the flame of a candle, it 

 becomes opaque, and crumbles down between the fingers. Before the blowpipe, it intumesces 

 into a white mass, and then melts into a transparent or pale rose-coloured globule. It readily 

 dissolves in, and gelatinizes with, nitric acid. If spirit of wine is burned upon the jelly, the 

 flame is coloured green. 



Composition. According to Klaproth, it is composed of silica 36.50, lime 35.60, boracic 

 acid 24.00, water 4.00. The Botryolite contains, according to the same chemist, silica 

 36.00, lime 39.50, boracic acid 13.50, o.\ide of iron 1.00, water 6.50. 



Geological Situation. This mineral occurs in fissures and cavities in the greenstone and 

 amygdaloid in New- York, and the contiguous parts of New-Jersey. 



localities. 



New-York County. This mineral is found in small quantities in cavities and veins in the 

 greenstone boulders which are strewed over various parts of the island. 



Rockland County. At Piermont, where the New-York and Erie railroad passes through 

 the greenstone, specimens of datholite have occasionally been found. They are highly modi- 

 fied crystals. The finest specimens have, however, been obtained from fissures in this range 



