Hydrous Silicate of Manganese and Calciuni. 499 



Genesis. — It is not possible at this time to present all 

 of the geologic data that bear upon the genesis of the 

 deposits in which orientite is persistently present. It 

 may be only briefly stated that the intimate association 

 of the manganese oxides and orientite with zeolites and 

 quartz, apparently without a pronounced interruption of 

 the process of deposition, indicates that the first group 

 have the same mode of origin as that commonly ascribed 

 to the second, i. e., deposition by warm hypogene waters. 

 It should be noted that this is essentially the mode of 

 origin suggested by Spencer in 1902,^*^* although the 

 evidence apears to be more conclusive at this time. 



m 



m 



m 



C. 



Fig. 5. Orientite from Cuba. 



Part 11. 



Crystallography. — Orientite crystallizes in the ortho- 

 rhombic system. It occurs as granular masses, as rosettes 

 of radiating prismatic blades, and as distinct crystals 

 making up drusy crusts. The crystals are small, the 

 largest not exceeding 1 mm. in length and the average 

 being very much less than this. There are two principal 

 habits which grade into each other. Crystals of the most 



^« Hayes, C. W., Vaughan, T. W., and Spencer, A. C, loc. cit., p. 63. 



