W. T. Schaller — Dumortierite. 215 



Fig. 2 shows variations from typical spherulitic form that 

 the fibers of dumortierite assume, a is four prisms irregularly 

 joined at the center, the ends spreading out into " brushes " of 

 fine fibers. This form is fairly abundant, b forms a prismatic 

 portion becoming fibrous at both ends, and while common in 

 the- New York, Arizona, and California occurrences is a rare 

 type for Washington dumortierite. c forms a sort of fan and 

 is composed of several " brushes " joined together. It is a 

 common type, d is an elliptical spherulite. e is a mass of 

 prisms such as b but not spreading out as a does. It is of 

 rarer occurrence, f is a bunch of radial fibers with no pris- 

 matic stem as in c. It is fairly common. 



Crystallo graphic. 

 The mineral is orthorhombic and from the various measure- 

 ments the following axial elements have been calculated : 



a = -8897 c = '6871 



The crystals were measured with the two-circle goniometer, 

 and the values for p and q , from which the above ratios are 

 obtained, are : 



^ = •7723 £ = -6871 



The forms observed are as follows : 

 b = oo = 010 

 a= oo = 100 



I = oo 2 = 120 



771 = 00 =110 



Besides these forms, reflections were obtained from several 

 other minute faces, but they were so minute and the reflections 

 so poor that their validity is very questionable and they are 

 omitted from the foregoing list. The average of the measured 

 angles compared with the calculated values are shown in the 

 following table : 



9 





t 



CO 



= 



320 



n 



= 



2 



CO 



= 



210 



d 



= 



i 







=z 



102 



V 



= 



2 

 3^ 







= 



203 



Letter. 



Symbol. 



Measured 





Calculated. 







d> 



P 







P 



b 



Oco =010 . 



0° 00' 



90° 



90' 



0° 00' 



90° 00 



a 



ooO =100 



91 23 





c 



90 00 



a 



I 



co 2 =120 



29 19 





c 



29 20 



a 



m 



co =110 



49 01 





t 



48 20 



u 



9 



J- oo =320 



59 49 





i 



59 19 



a 



n 



2 oo =210 



65 23 





i 



66 01 



a 



d 



iO =102 . 



91 21 



21 



46 



90 00 



21 07 



V 



f =203 



87 39 



26 



58 



a 



27 14 



The brachypinacoid is present on four crystals, usually as 

 broad faces. Some give relatively good reflections. 



