WOLFF AND PALACHE. — APATITE FROM MINOT, MB. 519 



muscovite ; more frequently it forms an irregular layer on the lepidolite- 

 muscovite crystals, showing, however, no parallelism with them ; and it 

 is rarely included in, and in small amount deposited upon, the apatite 

 crystals. In no case does the cookeite appear to have been formed at 

 the expense of any of the minerals previously formed in the cavity, 

 which are pei-fectly fresh and free from alteration. 



The apatite is implanted upon the quartz crystals and upon the lepido- 

 lite-muscovite crystals or the cookeite which covers them. As stated 

 above the apatite is embedded at times in the white quartz layer in 

 which it leaves sharp moulds when broken out, it having maintained its 

 crystal form despite the interference of the quartz. 



Finally a third generation of quartz in minute crystals is found as- 

 sociated with the cookeite, and rarely implanted upon the apatite 

 crystals. 



To briefly recapitulate the facts relating to the paragenesis of this 

 deposit we may say that we find : 



First, the crystallization of the smoky quartz, lepidolite, orthoclase, 

 and albite, the normal constituents of the granite, to form the walls of 

 the cavity. 



Second, the crystallization of muscovite, coating smoky quartz crystals 

 in part and the lepidolite crystals wholly. 



Third,, the crystallization of cookeite, coating muscovite, wholly or in 

 part. 



Fourth, the simultaneous crystallization of apatite and white quartz, 

 the latter confined to enlargement of smoky quartz crystals. 



Fifth, a second period of cookeite formation, accompanied by a final 

 deposition of quartz. 



Crystallography.* 



The apatite crystals are in genei'al of pronounced prismatic habit, 

 the average size beinsr about 1 cm. in height and 0.5 cm. in diameter. 

 Crystals larger than this are, however, common, the largest measuring 

 nearly 3 cm. in height and diameter. Crystals smaller than the average, 

 which are also numerous, tend to assume a more or less rounded habit 

 by nearly equal development of prismatic and terminal planes. 



The crystals are generally so implanted upon a terminal face that 

 one end has developed freely, and the fact that over three hundred 

 loose crystals with complete single termination and prism zone were 



* By 0. Palache. 



