248 



DESCRIPTIVE MINERALOGY. 



for by the delicacy of the crystalline groups employed. In other respects, the opinion that 

 the variety described above, and the acicular globules of pharmacolite, belong to the same 

 species, is grounded solely on the analogy of resemblance existing between the former with 

 crystals of gypsum, and between the latter and the radiated groups so frequently observed in 

 the same species." According to Dr. Turner, the crystallized mineral described by Haidinger 

 is composed of arsenite of hme 79.01, water 20.99.* 



LOCALITIES. 



A mineral apparently belonging to this species, has been found by Dr. Horton in magnetic 

 iron ore, in the town of Monroe, Orange county. 



ORDER IV. MAGNESIA. 



This order embraces the following minerals, viz : 



1. Brucite (Hydrate of Magnesia.) 3. Epsom Salt. 



2. Carbonate of Magnesia. 4. Magnesian Carbonate of Lime. 



5. Hydrobromate of Magnesia. 



BRUCITE. 



[In honor of the late Dr. Archibald Bruce, of New- York.] 



Brucite. BeudaiU. — Hydrate of Magnesia. Cleaveland, Phillips, T%omson and Slupard. — Native Magnesia. 

 Bruce. — Prismatic Talc-Mica, var. Jameson. 



Description. Colour white, inclining to green, and also grey. Streak white. It occurs 

 in plates which have a lamellar structure, and sometimes in prismatic concretions that point 

 to the regular six-sided prism. It is easily split into thin flexible laminae. Lustre shining, 

 and somewhat pearly. Semi-transparent in the mass, and transparent in single folia. Hard- 

 ness 1,0 to 1.5. Gives on paper a pohshed pearly trace. Specific gravity 2.35. Before 

 the blowpipe, it gives out water, but is not fusible. By the oxy hydrogen blowpipe, however, 

 small portions of it may be fused into an enamel. It is soluble without effervescence, in 

 dilute muriatic, nitric, and sulphuric acids. 



* Brewster's Edinburgh Jmmd of Science, III. 308. This volume also contains the paper of Mr. Haidinger, from which the above 

 extract is made. 



