WOLFF AND PALACHB. APATITE FROM MI NOT, ME. 521 



prism of the first order and the base, the edges modified by narrow 

 plaues of the forms a, s, r, x, and y. Crystals of this type are not 

 uncommon and often show double terminations. They merge, however, 

 by slight gradations into the second type, more characteristic for the 

 locality, shown in figures 2 and 3. Here the pyramidal planes become 

 more prominent and the most notable feature is the simultaneous occur- 

 rence of the right and left third order pyramids, giving the appearance 

 of the normal dihexagonal pyramid. 



The different forms may be characterized as follows : 



c (0001) always present, generally large, brilliant, and plane giving 

 perfect reflections. 



m (10T0) always present, generally dominant, brilliant, and generally 

 plane but sometimes faintly striated vertically. 



a (1120) generally present but narrow and commonly dull from deep 

 striatiou, the striae vertical and bounded by faces of adjoining plaues 

 of m. Occasionally the striations stop abruptly in the centre or near 

 the boundaries of a face as shown in figure 3, or they may be wholly 

 lacking, in which case the face is brilliant and "fives <rood reflections. 



h (2130) rarely developed and then narrow as shown in figure 4. 

 Surface plane, not involved in striations on a. 



r (10T2), x (10T1), and y (2021) all nearly always present with all 

 their faces, in varying proportions and often large, faces always brilliant 

 and free from striations, giving perfect reflections. 



w (7073) observed but once as a line face in the zone between y 

 and m. 



z (3031) generally present only as a deeply striated face, sometimes 

 very large as in figure 4, giving no reflection but determined by its 

 zonal relation to /x and fi-y. The striae bounded by faces parallel to 

 adjoining planes of m and y. Narrow faces of z giving faint reflections 

 sometimes present on the edges of the striae nearest to m. 



s (1121) always present with brilliant faces, often large. 



p. (2131) and /x t (3T21) are both present on many crystals, but vary 

 widely in size, quality, and regularity of development. Generally the 

 faces of both are dull and the forms are then indistinguishable. On 

 some crystals their faces are brilliant and reflecting but grooved or 

 pitted, and a constant difference in the character of these markings was 

 found by which, when they were not too far developed, the two forms 

 could be distinguished. On fx the markings ordinarily take the form of 

 sharp grooves parallel to the intersection of m and /x as shown in figures 

 2 and 3. The grooves seem to be in a way continuations of the striae 



