292 



/S. L. Penfield — Minerals from the 



crystal faces. The color is a sort of ash gray with a slight 

 reddish tone. Specimens of the gray tephroite associated with 

 the foliated red zincite from Franklin, !N". J., bear a most re- 

 markable resemblance to those of this pyroxene with the 

 alurgite. Before the blowpipe it fuses readily to a black bead 

 and imparts a yellow color to the flame. With the fluxes it 

 reacts for iron and manganese. It is insoluble in hydrochloric 

 acid. In thin sections under the microscope the presence of a 

 black ore, piedmontite, alurgite and numerous minute rutile 

 crystals could be detected. The pyroxene showed a prismatic 

 development, a large angle of extinction and a faint though 

 perceptible pleochroism ; in clinopinacoid sections for a very 

 pale rose, for c very pale blue. A section across the prism 

 showed the characteristic prismatic cleavage of pyroxene, and 

 in convergent light an optical axis, nearly in the center of the 

 field, the plane of the optical axes being the clinopinacoid. 

 Sections which approximated closely to the orthopinacoid also 

 showed in convergent light an optical axis ; all indicating the 

 pyroxene character. 



The material for the chemical analysis was crushed and 

 sifted to a uniform grain and separated by means of the barium 

 mercuric iodide solution. The material was not quite uniform 

 in specific gravity, and, therefore, fearing that it might be a 

 mixture, two portions were taken. The one for analysis A 

 varying between 3 382 and 3*338 and for analysis B between 

 3'338 and 3*257. These portions when examined with the 

 microscope were found to be quite free from impurities, the 

 heavier showing occasional particles of piedmontite and on 

 the whole somewhat clearer grains than those of portion B. 

 The analyses of the two portions are as follows : 





A. 



B. 



Mean. 



Ratio. 





CaMg(Si0 3 ) 2 . 



NaE(Si0 8 ) 2 



Si0 2 ___ 



54-39 



54-78 



54-59 



•910 





•264 



•646 



A1 2 3 -- 



9-93 



9-56 



9-74 



•095 ) 









Fe 2 3 _ 



11-78 



12*19 



11-99 



•075 \ 



•177 





•177 



Mn 2 3 . 



1-21 



•92 



1-06 



•007 ) 









MnO.. 



•66 



•50 



•58 



•008 ) 









MgO.. 



5-01 



5-06 



5-03 



126 \ 



•264 



•264 





CaO __ 



7*29 



7-19 



7-24 



•130 ) 









Na 2 . 

 K 2 .. 



9-40 

 •24 



9-24 

 •24 



9-32 

 •24 



150 | 

 •003 j 



•153 





•153 



Ign ... 



•38 



•35 



•37 











100-29 100-03 100-16 



The two analyses are so nearly alike that they will serve as 

 duplicates, showing that the material was quite pure and homo- 

 geneous. In calculating a formula, therefore, the ratio has 



