26 Dana and Wells — New mineral, Beryllonite. 



to note that eleven of the twelve prismatic planes have repre- 

 sentatives in the brachydome series, and, furthermore, they 



have nearly equal angles, since the axes a and c have approxi- 

 mately the same length. f 



Some idea of the complexity of 'the form may be gained 

 from fig. 8, which is a basal projection of a single crystal sim- 

 plified by the omission of several minute but distinct planes. 

 The prismatic faces are often narrow and by their oscillatory 

 combination produce vertical striations, especially on a; the 

 faces of the pyramid v also show sometimes striations parallel 

 to the edge v/j. The list of planes observed is given below ; 

 this might be increased if it were thought worth while to in- 

 clude a number of forms the symbols of which could not be 

 determined with accuracy. 



a (100,. i-i), b (010, i-*), c (001,^0); pri8ms g (410, i-l), h (310, i-3), i (210, i-2), 

 j (320, i-j), m (110, 7), k (230, i--), Z (120, i-2), ra(130, i-3), o(140, i-l), n (150, i-l), 



p (160, i-Q), q (1-12-0, i-12)- macrodomes d (102, |-i), e (101, \-i), / (201, 2-1) J 

 brachydomes a (014, J-i), /? (013, $-1), y (012, \-1), 6 (023, f-2), e (011, 1-1,), f (032, 

 f-2), v (021, 2-1), ■& (031, 3-i), k (041, 4-1), 1 (051, 54), fi (061, 6-1); unit pyramids 



ip (112, i), v (111, 1), s (221, 2), A (331, 3) ; macro-pyramids R (411, 4-4) ; u (212, 



3 3 



1-2), r(211, 2-2), 7(421,. 4-2); brachy-pyramids <A(232, 1--), 2(231, 3--); p(123, 



|-2), x (122, 1-2), u> (121, 2-2); a (132, f-3), a? (131, 3-3); 0(142,2-4), y (141, 

 4-4) ; 2 (151, 5-5) ; r (163, 2-6), <i> (161, 6-6). 



It will be noted that all the planes have very simple symbols, 

 and furthermore they are so tied together by zones that the 

 symbols of a large part can be determined without measure- 

 ment. The following are some of the prominent zones, after 

 the pinacoidal zones: e (101), u (212), v (HI), <p (232), w (121), 

 x (131), y (141), z (151), a> (161) ; also r (211), 6- (221), t (231) ; 

 again <p (112), x (122), a (132) Q (112) ; again m (110), ^ (231), 

 w (121), <r (132), e (011); again I (120), x (131), 0(142), e. 

 (011) and others. 



It is not thought worth while to give all the measurements 

 by which the planes were determined, since a greater accuracy 

 than 30' or 1° could in few cases be attained. For example, 

 in the brachydome zone we obtained : ca = 8°, c/3 = 10°f , 

 c r = 15°i, cd = 21°, ce = 29°, < = 39°, cy = 47° 41^', c#=59°, 

 cx = 65° 30', <?; = 70°, cfi = 73°-74°. 



The important calculated angles for the planes observed are 

 given in the following table : 



