- 1 8 Hon ess — Etching Figures of the 



from the three species named, it has many properties in 

 common with these species and may be comparable to 

 them. Calcite and rhodochrosite are much alike; smith- 

 sonite is comparable to none. This may be a sufficient 

 summation of the results of the HC1 solvent. 



A similar investigation of the five carbonates was made 

 with 10-percent HN0 3 . The calcite, magnesite, siderite, 

 and rhodochrosite figures were not noticeably different 

 from those produced by the HC1 of the same strength. 

 The smithsonite figures differed somewhat as they 'pos- 

 sessed a large basal plane, and the four bounding lines 

 slightly curved, giving the figure a rounded appearance. 

 The lateral faces are four in number and dip almost per- 

 pendicularly to the basal plane. The HC1 figure is com- 

 posed of but two planes meeting to form a basal groove, 

 with no distinct lateral faces ; hence the HN0 3 figures of 

 smithsonite differ from the HC1 etchings, and the same 

 comparison holds for both acids. 



If a cleavage piece of magnesite be immersed in hot 50- 

 percent HN0 3 for fifteen minutes, a figure is produced 

 which is much elongated and narrow; it is composed of 

 three faces forming a triangular pit, symmetrical to a 

 vertical plane. The bottom face may be present (see 

 fig. 16). 



For the last experiment upon these minerals, a con- 

 centrated citric acid was used, but its action upon siderite, 

 magnesite, and rhodochrosite was so slight that good 

 figures w T ere not obtained upon these minerals after 

 repeated immersions of long duration. The calcite rhom- 

 bohedron r etched beautifully after a half minute, the 

 figures being half as large as the rhombohedral face and 

 perfectly symmetrical (fig 17). They are composed of 

 two large faces, lying parallel to the shorter diagonal, and 

 two small faces, bounding the lower end of the figure. 

 The large faces are very smooth and represent, by their 

 position, the negative unit rhombohedron ; their inter- 

 sections with the surface of r are practically straight and 

 slightly divergent, until they reach the upper end of 

 the figure, where they converge abruptly forming two 

 rounded corners and a very blunt point; these faces 

 intersect to form the basal groove, which extends parallel 

 to the shorter diagonal. The two smaller faces dip quite 

 abruptly to the bottom of the figure ; the intersection of 

 these pianes with the two large ones is a curve, and the 



