CARBONATE OF MAGNESIA. 125 



frequently consists of minute acicular crystals ; aleo granular 

 and compact and in tuberous forms. Color white, yellow- 

 ish or grayish-white or brown. Luster vitreous ; fibrous 

 varieties often silky. Transparent to opaque. H=3 — 4£. 

 Gr=2.8— 3. 



Composition : carbonic acid 52'4, and magnesia 47-6. 

 Infusible before the blowpipe. Dissolves slowly with little 

 effervescence in nitric or sulphuric acid. 



Dif. Resembles some varieties of carbonate of lime and 

 dolomite ; but effervesces more feebly in acids, does not burn 

 to quicklime, and the light before the blowpipe is less intense. 

 The fibrous variety is distinguished from amianthus and other 

 fibrous minerals associated with it, by its greater hardness 

 and more vitreous luster, and from siliceous minerals gen- 

 erally by its complete solubility in acids. 



Obs. Magnetite is usually associated with magnesian 

 rocks, especially serpentine. At Hoboken, N. J., it occurs 

 in this rock in fibrous seams ; similarly at Lynnfield, Mass. ; 

 and at Bolton, imperfectly fibrous, traversing white lime- 

 stone. 



Uses. When abundant it is a convenient material for the 

 manufacture of sulphate of magnesia or Epsom salt, to make 

 which, requires simply treatment with sulphuric acid. 



brucite. — Hydrate of Magnesia. 



In foliated hexagonal prisms and plates. Structure thk 

 foliated, and thin laminae easily separated and translucent • 

 flexible but not elastic. Color white and pearly, often gray- 

 ish or greenish. H = l*5. Gi =2'35. 



Composition: magnesia 69-9, water 31*0. Infusible be- 

 fore the blowpipe, but becomes opaque and friable. Entirely 

 soluble in the acids without effervescence. 



Dif. It resemb'es talc and g \ psum, but is soluble in acids ; 

 it differs from heulandite and stilbite, also by its infusibility. 



Obs. Occurs in serpentine at Hoboken, N. J., and Rich- 

 mond Co., N. Y., also at Swinaness in Unst, one of the 

 Shetland Isles. 



Nemalite is a fibrous hydrate of magnesia or brucite. The 

 following are its characters ; 



Of what does magnesite consist? How is it distinguished from most 

 earthy minerals 1 How from calc spar"? For what -use is it fitted? 

 What is the appearance of nemalite 1 its composition ? its locality? 

 11* 



