472 DR T. THOMSON'S Analysis of some Minerals. 



Second Variety. 



I got this variety from the neighbourhood of Alston Moor, 

 under the name of Brown Spar. 



It has a dirty brown colour. Streak brown. 



Consists of small irregular rhomboids, with curve faces, and 

 entangled in each other. 



Lustre pearly, nearly dull. 



Opaque. 



Scratched by calcareous spar. 



Rather brittle. 



Specific gravity 3.404. 



The crystals were attached to a thin crust of brown matter, 

 having a pearly and splendent lustre. It was of the same na- 

 ture as the crystals, but had not like them been altered by ex- 

 posure to the weather. 



This specimen being subjected to a careful analysis, its con- 

 stituents were found to be, 



Carbonic acid, .... 18.50 



Protoxide of iron, . . 30.27 



Peroxide of iron, . . . 37.65 



Deutoxide of manganese, 4.75 



Water, 8.30 



99.47 



If we allow the manganese to be accidental, then the constitu- 

 tion of the mineral will be, 



1 atom carbonate of iron, . . 7.25 

 1 atom perhydrate of iron, . 6.125 



12.375 



It therefore constitutes a new species of iron-ore, which may be 

 distinguished by the name of Hydro-carbonate of iron. 



