14 0. C. Farrington — Chemical Comjwsition of Iolite. 



teristic pleochroism of the mineral. A determination of the 

 state of oxidation of the iron was included in the analysis, FeO 

 being determined by decomposition of a separate portion with 

 hydrofluoric and sulphuric acids and titration with potassium 

 permanganate. Water was determined directly, by fusing 

 about a gram of the mineral with dry sodium carbonate in a 

 Gooch tubulated crucible and collecting in a chloride of calcium 

 tube. The precaution was taken to surround the first crucible 

 with another containing sodium carbonate, so that no products 

 of combustion from the flame could penetrate the red hot 

 platinum and render the result too high. The analysis gave 

 the following results : 





I. 



II. 



Mean. 





Ratio. 





SiO„ .... 



49-44' 



49-56 



49-50 



•825 



•825 



5. 



A1.0, ... 



32-97 



33-04 



33-01 



.324 



- -326 



1-98 



Fe 2 O s ---- 



•35 



•41 



•38 



•002 



FeO 



5-11 



5-13 



5-12 



•071 



1 





MnO .... 



•32 



•27 



•29 



•004 



\ -335 



2-03 



MgO 



10-39 



10-46 



10-42 



•260 



i 





H 2 



1-65 



1-58 



1-62 



•090 



•090 



0-54 





100-23 



100-45 



100-34 





Sp. Gr. . . . 



2-607 













From this it will be seen that nearly all of the iron is present 

 as protoxide. The analysis also shows the ratio of Si0 2 : R„0 3 : 

 EG : H 2 0, to be very nearly 5:2:2: 0-5. 



In order to test these results by comparing different material 

 an analysis was also made of iolite from the well known local- 

 ity at Haddam, Conn., the specimens being very kindly fur- 

 nished by Prof. Geo. J. Brush from his private collection. 



This analysis resulted as follows : 





I. 



II. 



Mean. 





Ratio. 





Si0 2 .... 



4925 



49-03 



49-14 



•819 



•819 



5- 



A1 2 3 ... 



32-81 



32-87 



32-84 



•322 



-•326 



1-99 



Fe 2 0.... 



•58 



•67 



•63 



•004 



FeO .... 



5-06 



5-01 



5-04 



•070 







MnO .... 



•19 



•19 



•19 



•003 



- -333 



2-03 



MgO ... 



10-51 



10-30 



10-40 



•260 j 







H 2 0._._. 



1-81 



1-88 



1-84 



•102 ' 



•102 



0-62 





100-21 



99-95 



100-08 





Sp. Gr. .. 



2-610 













Here the percentages of Fe 2 3 and H,0 are slightly larger 

 than in the other analysis, but this might almost be expected 



