G. Palache — Powellite Crystals from Michigan. 369 



bluish-green color as the crystals, but the surface layer to the 

 depth of about three millimeters appears quite black and 

 opaque in reflected light and when examined in thin splinters 

 is seen to be colored a deep prussian blue. The boundary 

 between the two colors is not sharp but the darker portion 

 shades off rapidly into the lighter part. 



The dark-colored material is crystallized in a number of small 

 individuals, all in parallel position and showing approximately 

 the same forms as the crystals before described but with 

 greater proportional development of the forms e and h. 



An attempt was made to separate some of the darker mate- 

 rial for chemical examination, it being assumed that the lighter 

 colored part did not differ from the similar material analyzed 

 by Koenig and Hubbard ; but it proved impossible to obtain a 

 sufficient amount for any satisfactory tests. A small amount 

 (*051 gram) was however picked out in which there was a very 

 slight admixture of light-colored substance and a few minute 

 grains of epidote, and its specific gravity was determined to be 

 4*214. This determination is not wholly reliable on account 

 of the impurities and the small amount of material, and it is 

 probably too low ; but it seems to the writer fairly certain that 

 the specific gravity of the dark material is less than that of the 

 light (4-355). The specific gravity of the pure calcium molyb- 

 date has been calculated to be 4*267 (Melville), a value which 

 is rapidly raised by even small quantities of the tungstate. It 

 seems probable, in view of these facts, that the dark blue 

 material represents an occurrence of almost pure calcium 

 molybdate. It is much to be hoped that more material will 

 be found which will permit the chemical proof of the exist- 

 ence of this end member of the scheelite-powellite series. 



Miaeralogical Laboratory, 



Harvard University, February, 1899. 



