W. E. Ford — Interesting Beryl Crystals. 



221 



connection an analysis* by H. L. Wells of a clear and color- 

 less beryl found associated with gem tourmalines at Hebron, 

 Maine, might be quoted, which yielded Na 2 0, 1-13 ; Li 2 0, 

 1*60, and Cs 2 0, 3'60. These few instances would seem to 

 indicate that these unusually colored beryls are liable to con- 

 tain several per cent of alkalies, caesium being characteristi- 

 cally present. Their association with those tourmaline crys- 

 tals, which likewise contain unusual amounts of alkalies, can 

 hardly be considered entirely accidental, and consequently in 

 this fact of chemical similarity we probably find one of the 

 conditions which influence the association of this type of 

 beryl crystals with the gem tourmalines. 



Figure 7 is of a transparent green crystal (aqua- 7 



marine) in the Brush Collection from the Mack 

 Mine, San Diego Co., California, and is introduced 

 here chiefly for the sake of contrasting it with the 

 tabular type from the same general locality shown 

 in figure 2, the two crystals representing the 

 opposite extremes of development. The crystal is 

 represented in the figure in its true proportions, 

 except that its length parallel to the vertical axis 

 should be four times as great as is shown. The 

 length of the crystal is approximately fifteen times 

 as great as its diameter, the actual dimensions being 

 60 x 4 mm . The faces on the crystal are the prism of 

 the first order m, the dihexagonal prism i (2130), 

 the pyramid of the second order s and the pyramid 

 of the first order p, with the basal plane c, and are 

 developed with almost ideal symmetry. 



There are also in the Brush Collection two per- 

 fectly transparent and yellow colored beryl crystals 

 from Ramona, San Diego Co., which show remark- 

 able etchings : These are in the form of depressions 

 arranged singly in line, figure 9, or in groups, figure 

 10, in the positions which would naturally be occupied by faces 

 of the prism m. The prism m, however, does not appear on 

 the crystals, the groups of pits corresponding in position to 

 adjacent m faces being separated from each other by a dihexa- 

 gonal prism. Measurements of a series of the faces forming 

 the pits were made on a two-circle goniometer and the aver- 

 ages of the results obtained were used to plot the positions of 

 the faces on a gnomonic projection, figure 8, the plane of pro- 

 jection being taken as parallel to m (1010). From this pro- 

 jection figures 9 and 10 were made, which show the character 

 and arrangement of the etched pits drawn in orthographic 

 projection upon a plane parallel to m. The faces were all 



* Dana's Sys. Min. ; p. 407. 



