Genth and Pen field — Contributions to Mineralogy. 185 



Of these, the only faces which were suited for exact measure- 

 ment were on and f ' } b was bright but, owing to a fine vertical 

 striation, it gave a multiple reflection of the signal on the 

 goniometer. By taking advantage, however, of the perfect 

 clino-pinacoid cleavage, a face parallel to b was developed, 

 which gave a single reflection and, when tested on the goni- 

 ometer, exactly truncated the prism m. The measurements 

 from these faces, which were taken as fundamental are: 



m^m, 110 ^ 110 = 100° 12' 



f y\m, Oil >v 110= 65° 43' 



/ A b, 011 /s 0J0= 49° 5' 



from which the following axial ratio was calculated : 



d :b:c = -83623 : 1 : -88684, /J = 100 ^ 001 = 89 c 7£' 



The axial ratio established by Des Cloizeaux* for wolframite is ; 



d:b:c = -83000: 1: -86781, /3 = 89° 22' 



Besides the measurements given above as fundamental, the 

 only accurate measurement which could be made was 



f ^ m, 011 ^ 110 = 64° 32' calculated 64° 36' 



The faces in the prismatic zone are usually vertically stria- 

 ted. This is especially true of q, the obtuse edge of which is 

 rounded as indicated in the figure. Owing to these striations, 

 no exact measurements could be obtained from q ; however, 

 the symbol given above agreed best with the measurements and, 

 as will be shown later, this prism is prominent on crystals from 

 another locality. Possibly a pinacoid a, 100, i-l, oscillates with 

 q but no distinct reflection was obtained from the striated part 

 to indicate its existence. With the exception off, the faces 

 which terminate the crystals are usually poorly developed; co 

 was determined by approximate measurements only ; t usually 

 gave no reflection whatever. 



Cleavage sections, parallel to b, show with the polarizing 

 microscope an extinction, inclined about 17° from the vertical 

 axis, in the obtuse angle /?. This direction corresponds to the 

 axis of least elasticity c. In convergent polarized light an 

 obtuse bisectrix could be seen, but the section was too small to 

 admit of a measurement of the angle of the optical axes. The 

 sections transmit a brown light. The pleochroism is marked ; 

 for rays vibrating parallel to c green ; parallel to b yellowish 

 brown, but varying somewhat, even in the same section. An 

 increase of color is probably due to a slight percentage of FeO, 

 the lighter colored material is probably nearly pure Mn"W0 4 . 



* Ann. Chimie et Phys., IV, xix, p. 168, 1870. 

 Am. Jour. §gi.— Third Series, Vol. XLIII, No. 255.— March, 1892. 

 12 



