CALIFORNIA ACADEMY OF SCIENCES. 7 



b ( — P) on all but one, and t (oo P 2) on all but two. Very 

 commonly present are g (o Pj, h (2 P oo), i (P oc), n (oo P oo), 

 z (oo P 2), o (2 P 2), e (3 P |), ra (— 3 P 3), and U (6 P oo). 

 r (f P |) was met with on five, x (3 P 3) and ff ( — 3 P) on four, 

 Y (4 P oo) and & (3 P 3) on three, fe (— 3 P 3) and X (— 2 P oo) 

 on two, while H (oo P 3), J (oo P $), P (oo P *%), £ (— V- P). 

 Q (4 P 2), and B (4 P 4) were found each on but a single crystal. 

 The largest number of forms met with on any one crystal was 

 nineteen (Fig. 2, PL I), and the smallest number nine (Fig. 9, 

 PL III). 



The habit of colemanite is from medium to short columnar, 

 determined by the large development of 8 (oo P). None of the 

 other lateral faces are ever large. Among the terminal forms 

 g (0 P), h (2 P oo), b (— P), y (P), v (2 P), c (P oo) and a 

 (2 P oo) frequently occur largely developed, d (2 P 2) rarely, and 

 a; (3 P 8) and oo ( — 3 P 3) in but a single instance. The remain- 

 ing forms, and at times some of those just enumerated, occur 

 with from small to extremely minute faces replacing the edges 

 of the more developed forms. 



In a general way it may be said of the crystals of colemanite, 

 that they appear in three different habits, determined by the 

 considerable or moderate development of g (0 P) and /i(2P oo), 

 or by their total absence. The two extreme types, at least, are 

 quite pronounced. In the one (Fig. 1, PL I) g (0 P) and 

 h (2 P oo ) are very largely developed, while all the rest of the 

 terminal faces are small. The faces in the zone of the clino- 

 diagonal polar edge of y (P), (d. y. i.) are very small in cry- 

 stals of this type, so that, with the gentle inclination of g 

 (0 P) to the front, and the sharp inclination of h (2 P oo) to 

 the rear, the crystal assumes a strikingly monoclinic habit. 

 When, however, g (0 P) and h (2 P oo) disappear entirely, the 

 forms of the zone d. y. i. at once strongly develop (Fig. 3, PL I). 

 It then results that, from the curious fact that g (0 P) and 

 i (P oo) have nearly the same inclination to the vertical axis, 

 the crystal may assume, with a certain development of the forms, 

 a strikingly rhombic habit; and in any event one is liable to fall 

 into error by interpreting i as the basal pinacoid, and g as the 

 positive hemidome. 



