212 LARSEN AND WHERRY: LEVERRIERITE FROM COLORADO 



Effect of dehydration on the optical properties. In order to 

 determine the effect of dehydration on the crystal structure, 

 samples of coarse powder were examined microscopically after 

 being heated respectively for 8 hours at 65°, 5 hours at 130°, 

 2 hours at 290°, and 2\ hours at 360°. The loss of so large an 

 amount of water would lead one to expect considerable change 

 in the properties. However, the optical properties remained 



TABLE 2 



Effect of Dehydration on the Optical Properties of Leverrierite from 



Colorado 



° The apparent value as measured by the immersion method immediately 

 after imbedding in an oil of that index of refraction. 



practically unchanged up to 360°C, and there was only a moderate 

 decrease in the indices after heating for half an hour at redness. 

 The results are presented in Table 2. The mineral remains sensi- 

 bly uniaxial, even after heating to redness, and the optic axis 

 emerges normal to the plates. On heating, it gradually loses its 

 waxy luster and becomes somewhat darker in color and more 

 strongly pleochroic. It increases in hardness slightly and be- 

 comes rather brittle. The perfect cleavage becomes even more 

 prominent than before dehydrating. 



