4:28 Ford — Chemical Coraijosition of Dumortierite. 



the material that was analyzed. The exact locality from which 

 the mineral came could not, however, be learned. This mate- 

 rial shows a marked difference in appearance from that of 

 dumortierite from other known localities, as it has a pro- 

 nounced lavender color rather than blue. The pleochronism 

 of this type is analogous to other dumortierite, but ranges from 

 deep lavender to colorless instead of from deep blue to color- 

 less. The optical orientation of the crystals is the same as in 

 the case of the dumortierite from Clip. It occurs in masses 

 of considerable size, of radiating columnar structure, associ- 

 ated with granular quartz and a light colored mica from which 

 it was easily separated by means of the heavy solutions, and 

 thus obtained in a pure condition. 



Method of Analysis. — The method of analysis presents no 

 new features and need be only briefly discussed. The silica, 

 alumina, and ferric oxide were determined as usual. Boron 

 was determined by the Gooch method"^ using the precautions 

 suggested by Penfield and Sperrv, recorded in their paper on 

 the Composition of Howlitef and by Penfield and Foote in 

 their paper on the Composition of Tourmaline. :j: It was found 

 that water could not be determined by simple loss on ignition 

 and, accordingly, the method suggested by Penfield§ of igniting 

 with a weighed quantity of lime, was employed. The loss on 

 ignition in this case was found to be less than when the min- 

 eral was ignited alone. A somewhat different method of 

 analysis had to be adopted in the case of the dumortierite 

 from Harlem on account of the small amount of material 

 available, and it is fully realized that the results are not to be 

 looked upon as being as exact as those of the other analyses. 

 The analysis was made on only 0*6 gr. of the mineral, which it 

 was necessary to divide into two portions. In one of these, 

 water was determined in the manner described above, and in 

 the other boric oxide and the remaining constituents, silica, 

 alumina and ferric oxide. 



The results of the analyses are as follows : 



Analysis No. I. Dumortierite from Clip, Arizona. 

 Specific gravity close to 3 '319. 













Average. 



Eatios. 





SiO, . 



30-00 



29-66 



29-91 



29-86 



-497 





Al.O, 



63-20 



63-74 



63- 



76 



63 56 



•617X6 = 



= 3-702 



Fe^O, 



-23 



-23 







•23 



•001X6 



•006 



B,0,- 



5-47 



5-06 







5^26 



•070X6 



•420 



h:o 



.1-45 



1-38 







1*41 



•070X2 



•140 





100-32 



4-268 







4-268 : 



•497 



= 



60:6-99 







* Amer. Cliem. Jour. , ix, 33. f This Journal (3). xxxiv. 220, 1887. 



X Ibid. (4), vii, 97, 1899. § Ibid. (3), xxxii, 109, 1886. 



