126 SALTS OF MAGNESIA. 



Neatly fibrous and silky ; fibres brittle and easily sepera- 

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

 but becomes opaque and crumbling 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. 



Qbs. 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 



x^ 



translucent and seldom more than a quarter of an inch 

 through. Color white or grayish ; sometimes yellowish or 

 greenish. Luster vitreous. H=7. Gt=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. 



Nitrate of Magnesia. Occurs in white deliquescent efflorescences, 

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



What is Brucite 1 What is its appearance ] 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 1 What is its mode of occurrence 1 



