290 S. L. Penfield — Minerals from the 



that its pleochroism is not very marked ; the axial colors for a 

 and c are red with a purplish cast, for b brownish red. 



Before the blowpipe alurgite first swells and then fuses at 

 about 3 to a slightly yellowish, blebby glass and gives a faint 

 potash flame. With sodium carbonate in the oxidizing flame 

 a green bead, Mn, but with borax a violet color is only ob- 

 tained after adding a large quantity of the mineral, indicating 

 that the amount of manganese is not very great. In the 

 closed tube at high temperature neutral water is given off. 

 The finely powdered mineral is almost absolutely insoluble in 

 boiling concentrated sulphuric or hydrochloric acids. After 

 fusion it is also insoluble. The specific gravity of a number 

 of pieces was taken by means of the heavy solution, and 

 found to be between 2*835 and 2*849. Breithaupt gives 

 2-984- 3-00. The hardness is about 3. 



The results of the analysis of the air dry powder are given 

 below under A. Under B we have the same after calculating 

 Fe 2 3 and Mn 2 3 as A1 2 3 , MnO as MgO, JSTa 2 as X 2 and 

 recalculating to 100 per cent. 





A. 



B. 



Si0 2 .... 



53-22 



53-57 



A1 2 3 ... 



21-19 



22-68 



Fe 2 3 ___ 



1-22 





Mn 2 3 __. 



•87 





MnO.... 



•18 





MgO...- 



6-02 



6*16 



K 2 



11-20 



11-80 



Na 2 0___. 



•34 





HO..... 



5-75 



5-79 



9 -h9 



Ratio. 

 •893 

 •222 



Si0 2 



(AIOH)O . 



•893 

 •444 



•154 

 •125 



(MgOH) 2 

 K 2 



•077 1 

 * 125 ^.224 



•643 



H 2 



•022 J 



99-99 100-00 



The water was determined as loss on ignition, and that it is 

 present in the mineral as hydroxyl is shown by the following 

 fractional determinations : 



Two 



hours 



at 100° 



C. 



0-74 



a 



a 



" 200 



u 



0-48 



it 



u 



" 300 



it 



0-17 



Total 1-39 per cent loss. 



The iron was found to be all ferric and, moreover, when 

 weighed quantities of the mineral and ferrous sulphate were 

 dissolved together in sulphuric and hydrofluoric acids, and 

 titrated with potassium permanganate, it was found that some 

 of the ferrous sulphate was oxidized by the mineral, which 

 must have resulted from the presence of a higher oxide of 



