RE-EXAMINATION OF AMERICAN MINERALS. 117 



The following are the results of our analyses. Nos. 1 and 

 2 were foliated ; Nos. 3 and 4 were of the radiated variety: 



1 2 8 4 



Magnesia 66.30 66.25 42.30 44.00 



Protoxide of iron 60 1 1QQ trace trace 



Protoxide of manganese., trace j 



Carbonic acid 1.27 trace 36.74 36.60 



Water 31.93 32.75 20.96 19.40 



Direct determination of water 20.10 



The foliated variety gives the exact composition of brucite. 

 In two determinations of loss by heat the numbers 34.30 and 

 35.67 were obtained; great difficulty was found in obtaining 

 the brucite perfectly pure, owing to its intimate association 

 with the hydro-magnesite. 



The radiated variety (as before stated) gives the composition 

 of hydro-magnesite, and to show that the original analyses were 

 made from a mixture of these minerals we give Dr. Erni's re- 

 sults* for comparison : 



Mg Fe H Total. 



50.01 1.01 27.07 21.60 99.69 



50.72 .96 26.85 21.47 100.00 



9. Hydro-magnesite found crystallized. 



The hydro-magnesite above mentioned is extremely beau- 

 tiful, and in appearance resembles very much the thomsonite 

 from Kilpatrick in Scotland. Its structure is highly crystal- 

 line, and in some instances forms distinct crystals, which have 

 been considered as monoclinic (?) (Dana) ; the diagonal cleav- 

 age is very distinct ; hardness 3-3.5 (scratching calcite with 

 ease); specific gravity 2.145-2.18. It occurs at Wood's Mine, 

 Texas, Lancaster County, Pa., in seams which are sometimes 

 half an inch in thickness, and at Low's Mine in veins generally 

 from one tenth to one fifth of an inch wide, having a beautifully 

 radiated structure. The results of two analyses of a specimen 

 from Wood's Mine are as follows : 



1 2 



Magnesia 43.20 42.51 



Carbonic acid 36.69 35.70 



Water 20.11 21.79 



Iron and manganese., trace trace 



* From Dana's Mineralogy, p. 213. 

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