204 lioness — Etching F'ujtbres of the 



and in fact etched, but the rhonibohedral crystals, whose 

 surfaces are curved, did not reveal well-defined etchings, 

 and consequently were rejected. The best results were 

 obtained on brown rhonibohedral cleavage plates from 

 Greenland, which, if cleaved sufficiently thin could be 

 readily examined under the microscope. 



The smithsonite used for this purpose was obtained 

 from Altcnberg, Saxony ; it occurs as a crust of exceed- 

 ingly small transparent rhonibohedral crystals, possess- 

 ing a high luster and fairly smooth faces. The rhonibo- 

 hedral faces are decidedly the better although the unit 

 prism did occur on several, sufficiently developed, as to 

 permit of etching. 



Rhodochrosite also could be obtained only in rhoni- 

 bohedral form, so that brilliant cleavage fragments from 

 Alicante, near Leadville, Colorado were used for the pur- 

 pose of etching. 



From the foregoing, it will be readily understood that 

 the chief difficulty in the comparison of this isomorphous 

 series of carbonates lies in the rarity of forms desired, 

 and as the only available material did not possess the 

 necessary variety, a comparison of the one form only 

 must of necessity be more or less incomplete. Neverthe- 

 less the results obtained are interesting, and may be 

 accepted as a minor contribution to the vast literature 

 on etch figures. 



The Cumberland calcite described above, upon immer- 

 sion in 10 percent dil. HC1 for a period of a few seconds, 

 revealed a great difference in the solubility of the various 

 faces. The unit rhombohedron was the first form to etch,, 

 followed immediately by the unit prism ; the second order 

 prism, when present, etched later ; but the scalenohedron 

 strangely enough, did not etch at all. One could hardly 

 say that the face had not been acted upon by the acid, 

 because it was very apparent that the face had undergone 

 a change, as the edges were rounded and the whole face 

 appeared glassy but not revealing the slightest indication 

 of an etch pit. Repeated immersions produced good fig- 

 ures upon the rhombohedron and the unit prism, also 

 upon the second-order prism, but still the scalenohedron 

 maintained its glassy luster and did not decrease much in 

 size, and only disappeared through the action of the sol- 

 vent, after the other forms had been completely corroded 

 and eaten aw T ay. 



