554 



SAMUEL WEIDMAN 



the Retger's solution the fayalite from the iron oxide, as the two 

 were so intimately mixed by alteration and intergrowth. The iron 

 oxide, which was strongly magnetic, was very largely removed by 

 means of a magnet, and finally sorting out the honey-yellow fayalite 

 from the magnetic iron oxide by hand had to be resorted to. After 

 considerable work, 0.3610 grams of the nearly pure fayalite was 

 separated, which was analyzed by Dr. Victor Lehner, and found 

 to be as follows: 



SiO, ------- 33-77^ 



Ve^O^ - - - - - - 0.23 



FeO - - - - - - - 62.09 



Undetermined ----- 3.91 



100.00 

 The materials associated with the fayalite, and necessarily included 

 in the analysis, were small particles of feldspar, quartz, pyroxene, 

 and amphibole. The undetermined portion in this second analysis, 

 3.91 per cent., as indicated by comparison with the first rough analysis, 

 is very probably mainly alumina and the alkalies which may be 

 assumed to be combined with perhaps 4 or 5 per cent, of silica to 

 form the associated silicate minerals. An additional source of silica, 

 probably i or 2 per cent., was due to small included fragments of 

 quartz. After deducting, therefore, an amount of silica — 6 or 7 per 

 cent. — present in mineral other than fayalite, it will be seen that the 

 ferrous oxide and silica occur in approximately the proportions 

 found in fayalite. 



Under the microscope the fayalite has the appearance of this 

 mineral as usually described. In ordinary light it has a light stone 

 color, with yellowish-green or honey-yellow tints. It is distinctly 

 pleochroic, the green tinge changing from a light to a darker shade. 

 The double refraction is strong, probably stronger than for olivine. 

 It apparently has two fairly well-defined planes of cleavage, as 

 illustrated in Fig. i, which are probably parallel to the pinnacoids, 

 001, and 010. 



The fayalite occurs in the quartz-syenite, having a silica content 

 of 61.18 per cent., and to a very small extent in the amphibole granite, 

 bearing 67.99 per cent, silica. In phases of the quartz syenite it 

 probably constitutes from i to 5 per cent, of the rock, and was noted 



