66 Mr. T. S. Hunt^s Description and Analysis of Loganite, 



on the acute and obtuse lateral edges, also on the acute solid 

 angles. The edges are generally rounded, and the secondary 

 planes not well defined. Cleavage with the sides and base of 

 the prism distinct, with the macrodiagonal imperfect. 



Hardness 3. Specific gravity 2*60 to 2-64. Lustre of the 

 cleavages vitreous, shining, the surfaces of the crystals generally 

 dull. Colour clove-brown to chocolate-brown, streak and powder 

 grayish-white, sub-translucent, brittle, fracture uneven. The 

 crystals, which are short and thick, are generally small, and so 

 penetrated with the calcareous gangue, that great care was ne- 

 cessaiy in selecting specimens for analysis. 



The powdered mineral exposed to heat in a tube gives off a 

 large quantity of water with an empyreumatic odour. Before 

 the blowpipe it loses its colour, becoming grayish-white, but 

 does not fuse ; moistened with cobalt solution and ignited, it 

 becomes blue. Acids take up magnesia, alumina and peroxide 

 of iron with a small but variable trace of lime, which exists as a 

 carbonate derived from the gangue, and leave pulverulent silica ; 

 the decomposition by this means is not, however, complete. 

 Qualitative analysis showed the presence of no other ingredients 

 than those already indicated, with the exception of a feeble trace 

 of manganese. Regard was had in the examination to the de- 

 tection of the rarer earths, the alkalies, titanic and phosphoric 

 acids. 



The finely pulverized mineral was heated to whiteness, and 

 the loss thus sustained regarded as water, with the trace of car- 

 bonic acid, which was so small as to be difficult to determine 

 directly upon the portions of the mineral which my specimens 

 afforded me. The further decomposition was effected by fusion 

 with carbonate of soda, and the silica and bases were separated 

 by the usual methods. In analyses upon three different speci- 

 mens were obtained — 



Sihca . . . 

 Magnesia . . 

 Alumina . . 

 Peroxide of iron 

 Water and C0« 

 Lime . . . 



L II. III. 



32-84 3214 3317 



3512 36-43 



13-37 13-00 



2-00 2-28 



1702 16-83 16-50 



•96 -93 



101-31 101-61 



If we subtract from the loss by ignition the amount of the 

 carbonic acid requii-ed to form a carbonate with the lime, we 

 have respectively 16-36 of water and 1*70 of carbonate, and 

 16*12 of water and 1-64 of carbonate. Calculating the oxygen 

 ratio between the silica and the bases, we have for the first ana- 



