128 



SALTS OP MAGNESIA. 



Neatly fibrous and silky ; fibres brittle and easily sepera. 

 ble. Color whitish, grayish or bluish white ; transparent, 

 but becomes opaque and ciumbling on exposure. H = 2. 

 Gr = 2-35— 2-4. 



Composition : magnesia 62*0 ; protoxyd of iron 4-6 ; water 

 28*4 ; carbonic acid 4*1 ; — (Whitney.) In the flame of a 

 candle the fibres become opaque, brownish and rigid, and in 

 this state easily crumble in the fingers. Phosphoresces with 

 a yellow light when rubbed with a piece of iron. 



Dif. Resembles abestus or amianthus, but differs in 

 becoming brittle before the blowpipe. 



Obs. Occurs in serpentine at Hoboken, N. J., in green- 

 stone at Piermont, Rockland Co., N. Y., and Bergen Hill, 

 N. J. 



Hydromagnesite. A pearly crystalline, or earthy white 

 pulverulent hydrous carbonate of magnesia, from Hoboken, 

 N. J., and Texas, Pa. 



boracite. — Borate of Magnesia. 



Monometric. Cleavage octahedral ; but only in traces. 

 Usual in cubes with only the 

 alternate angles replaced ; or 

 having all replaced, but four 

 of them different from the oth- 

 er four. The crystals are 

 translucent and seldom more than a quarter of an inch 

 through. Color white or grayish ; sometimes yellowish or 

 greenish. Luster vitreous. H=7. Gr=2*97. Becomes 

 electric when heated, the opposite angles of the cube be- 

 coming of opposite poles, one north and the other south. 



Composition : boracic acid 70*0, magnesia 30*0. Intu- 

 mesces before the blowpipe and forms a glassy globule, 

 which becomes crystalline and opaque on cooling. 



Dif. Distinguished readily by its form, high hardness, 

 and pyro-electric properties. 



Obs. Boracite is found only with gypsum and common 

 salt. It occurs near Luneberg in Lower Saxony, and near 

 Kiel in the adjoining dutchy of Holstein. 



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Nitrate of Magnesia. Occurs in white deliquescent efflorescences, 

 having a bitter taste, associated with nitrate of lime, in limestone cav- 



What is Brucite? What is its appearance 1 How is it distinguished 

 from talc, gypsum, and other minerals 1 What is said of the crystals of 

 boracite ? What is stated of its electric properties? What is its com- 

 position ? What is its mode of occurrence 1 



