210 Hon ess — Etching Figures of the 



groove is due to solution along the cleavage plane, and 

 the direction of the deeper depressions is governed pos- 

 sibly by microscopic striations. 



The figures, while they are generally rhombic, vary a 

 little in shape: some of the forms are considerably 

 rounded, while others are quite angular (see fig. 5). The 

 larger angle of the rhomb measures, for an average of 

 eleven readings, 136° and the longer diagonal of the fig- 

 ure extends in a direction approximately 27° with the 

 prism edge. The two longer sides vary but 7° from a 

 parallel position with the prism edge ; thus it is readily 

 seen that the figures are not only asymmetric, but asym- 

 metrically placed as well. While the figures are simple 

 they are unique in that any one of the four faces may be 

 extended as a groove at the acute angle, and appears as 

 an appendage curved toward the figure and varying in 

 length with the stage of development. Very often a fig- 

 ure contains two, one at each acute angle. The general 

 direction of these modifications is always parallel to the 

 prism edge. The majority of the figures possess but two 

 curved planes, meeting at the bottom of the pit to form 

 a line parallel to the longer diagonal (see fig. 4). Closer 

 observation reveals a direct connection between the two- 

 winged form and the larger grooves mentioned above ; in 

 many instances a large figure can be seen occupying the 

 end of the elongated depression, with the attached 

 appendage on either side, extending outward to the edge 

 of the groove, and turned in direction opposite to that 

 in which the groove is proceeding. Thus it seems to 

 be a peculiar manner of growth, which continued with 

 repeated immersions. Those figures possessing the 

 attachments turned in opposite direction on two parallel 

 sides, usually develop the smaller groove which extends 

 across the prism face at an angle of 45°. 



The figures produced on 1120 by concentrated citric 

 acid are much less symmetrical than the HC1 figures, they 

 are more rounded and slightly elongated, but their gen- 

 eral direction is quite the same. They are composed of 

 two warped faces intersecting in an S-shaped curve and 

 asymmetrically placed. The canals or grooves which 

 occur on the prism etched by HC1 also occur on this 

 crystal etched by citric acid and are produced in a 

 like manner. 



Another crystal was etched with a cold 25-percent citric 



