﻿British Mineralogy. 329 



perfect and hackly; brittle; hardness 5*5, scratching apatite, 

 but scratched by orthoclase. 



The specific gravity, determined by weighing a large specimen 

 (2024*5 grs.) out of and in distilled water, was found to be 3*431. 

 Another determination, made upon 38*26 grains in the powdered 

 state, gave 3*436 spec. grav. at 60° F. After ignition for some 

 time at a red heat, the mineral, which had lost 0*729 per cent., 

 was found to possess a specific gravity of 3*474. 



The blowpipe characters were found to be as follows : — Heated 

 in a close or open tube it remains unaltered in appearance, but 

 evolves a little water, which is probably only hygroscopic ; if in 

 larger fragments, it occasionally decrepitates. After heating, it 

 reacts alkaline to reddened litmus and turmeric test-papers 

 moistened with distilled water. 



Heated alone in the blowpipe-flame, either in the platinum 

 forceps or on charcoal, it melts at a pretty strong heat under 3 

 of Von Kobell's scale, quietly, without intumescence, to a brilliant 

 black globule which is not magnetic ; with soda alone in the re- 

 ducing flame it also fuses with escape of gas to a black non-mag- 

 netic globule ; on platinum-foil with soda and nitrate of potash 

 in the oxidating flame it affords the characteristic green reaction 

 of manganese. 



With borate on platinum wire in the oxidating flame it dissolves 

 completely to a clear reddish-yellow glass, which becomes colour- 

 less on cooling, and in the reducing flame on charcoal produces a 

 greenish glass. With phosphate it gives the same colour-reac- 

 tions as with borate, both in the oxidating and reducing flames; but 

 in this case a skeleton of silica remains in the glass undissolved 

 by the phosphate. 



It is not, or at least very imperfectly, decomposed by acids. 

 The chemical analysis was conducted as follows : — The amount 

 of ignition loss was determined upon 38*40 grs., and after heat- 

 ing for twenty minutes to redness found to be 0*28 gr., equivalent 

 to 0*729 per cent. 20*01 grs. of the mineral in fine powder 

 were fused in a platinum crucible with 80 grs. carbonate of soda 

 n potash; a strong manganese reaction was observed. The 

 fused mass was decomposed by hydrochloric acid, evaporated in 

 a water-bath to dryness, and then heated in an air-bath to render 

 the silica insoluble ; the silica, after being well washed and ig- 

 nited, weighed 7*83 grs.. or 49*12 per cent, of the mineral; its 

 purity was tested by being dissolved, in a silver basin, in a solu- 

 tion of carbonate of soda, when only an inappreciable trace of 

 oxide of manganese was found to remain insoluble. 



The filtrate was thrown down by ammonia, and the alumina 

 separated from the oxides of iron and manganese by potash ; 

 after reprecipitation and ignition it weighed 0*33 gr., equal to 



