THE MINERALS OF IDAHO 



381 



chlorite. This chlorite is biaxial and negative with 2V nearly 0°. 

 The refractive indices are a =1.650, and 7=1.660. The pleo- 

 chroism is X = pale brown, Y and Z = green. The chlorite was sep- 

 arated for analysis from the chloritoid and the associated muscovite 

 by means of an electromagnet and heavy solutions. This was ana- 

 lyzed but the presence of several per cent of cobaltiferous arseno- 

 pyrite in dusted very minute grains in the sample was not suspected 

 and the analysis was somewhat upset by its presence, as in the case 

 of the chloritoid. After being corrected as well as possible for the 

 several errors arising from this cause, it was recalculated to 100 per 

 cent, yielding the following results and ratios: 



Analysis (recalculated) and ratios of chlorite 

 [E. V. Shannon, analyst] 



These ratios yield the formula 6(Fe,Mg)0.2Al 2 3 .3Si0 2 .5H 2 0. 

 This chemically is very similar to some prochlorites. The formula 

 is identical with that obtained for an analysis of corundophilite from 

 Chester, Mass. The optical properties, both the optical character and 

 the high refractive indices, are different from most of the minerals of 

 the group. 



SHOSHONE COUNTY 



A specimen labeled pegmatite from 2J^ miles south of Trimmed Tree 

 Hill in the Avery quadrangle consists mainly of feldspar and chlorite 

 with less cyanitc, tourmaline, and biotite. The chlorite is dull green 

 and coarsely foliated in the hand specimen. Under the microscope 

 it is biaxial positive with 2V approaching zero, acute bisectrix per- 

 pendicular to the plates. The color is so pale that the pleochroism 

 in tones of brownish green and brownish blue-green is not marked. 

 The refractive indices, a and /3 are 1.59.") ±0.003. This chlorite is 

 probably intermediate between clinochlore and amesite, approaching 

 the latter. 



A specimen from the Sherman mine on Pine Creek contains a very 

 fine scaly deep green chlorite surrounding ankerite rhombohedra up 

 to 2 cm. on an edge or replacing fragments of gray quartzite included 

 in the quartz of the vein. Other minerals associated with the chlorite 

 are pyrite and pyrrhotite which apparently are later. Under the 

 microscope the chlorite is very fine granular with very low birefring- 

 ence. It is apparently biaxial negative with 2V nearly 0°. The, 



