154 Field Columbian Museum — Geology, Vol. III. 



were accordingly obtained as follows, the ratios of Washington and 

 Phillips being given for comparison: 



a : b : c = 0.95873 : 1 ; 0.691 14, Farrington and Tillotson. 



a : b : c = 0.9573 : 1 : 0.6894, Phillips. 



a : b : c = 0.9396 : 1 : 0.6726, Washington. 



The total forms observed with the measured and calculated angles 

 are as follows, new forms and fundamental measurements being 

 marked with an asterisk: 



No marked pleochroism of any of the crystals could be observed. 

 On examination of some of the acicular forms with the polarizing 

 microscope the usual characters were observed with the exception that 

 a red variety occurred which does not seem to have been hitherto men- 

 tioned. These crystals are characterized by a brownish-red color, 

 occur in tufts, and the individuals average from .5 to 2 mm. in length. 

 They are transparent and of marked brownish-red color but show 

 little or no pleochroism. 



ORP1MENT 

 MERCUR, UTAH 



PLATES XLIV AND LIII 



Among the specimens obtained from Maynard Bixby, orpiment 

 from Mercur, Utah, was represented by an especially notable one, 

 (Mus. No. M 8206). This specimen consisted of a piece of limestone 

 about 3x4 inches in size, upon which were implanted about fifteen 

 large crystals of orpiment together with fragments of orpiment 

 crystals and numerous crystals of calcite. The size and perfection 

 of many of the orpiment crystals seem to exceed any that have 



