WRIGHT: CHANGE IN ANGLES OF QUARTZ 



493 



minations of the mean specific heats of quartz at 100°, 300°, 500°, 

 550°; also of the mean specific heats of two normal silicates, albite 

 and microcline, which do not have low temperature inversion points. 

 From these values the total heats were computed. The specific 

 heats of quartz were consistently higher than those of albite and 

 microcline which behave like other normal silicates in their specific 

 heat values. The differences between the total heats of quartz 



100 



0° 100 



EXPANSION 



SPEC. VOL. 



200" 300" 



CRYSTAL ANGLE 



BIREFRINGENCE 



400" 500° 

 SPEC. HEAT 



Fig. 2 



and microcline for the different temperatures are plotted in figure 

 2. The general shape of this curve is similar to that representing 

 the change in crystal angles except that its curvature is greater 

 and approaches that of a circular arc. Altho part of this differ- 

 ence in shape may be due to experimental error in the different 

 sets of values yet it is an appreciable difference and may express 

 relations of which we are at present unaware. It is evident, how- 

 ever, that in a general way the relative changes in the crystallo- 

 graphical and optical properties of quartz with temperature follow 



