202 1 Ion ess — Etchin g Figures of th e 



Siderite reveals the same peculiarities; occasional 

 asymmetric forms accompanied by many symmetrical 

 ones. Baumhauer 2 observed only monosymmetric forms, 

 Dilute HC1 produced figures very similar to magnesite, 

 1ml which do not resemble so closely the siderite figures 

 obtained by the writer, which, although long and mono- 

 symmetrical and pointed, are bounded by two long curved 

 sides which are absent in Tschermak's. According to 

 Tschermak, the number of asymmetric forms occurring is 

 greater than that on magnesite, and many are enantio- 

 morphic. ELS0 4 produced triangular forms, the most 

 of which are monosymmetric, — a few asymmetric, reveal- 

 ing a complex crystal, or at least a doubtful result due 

 probably to a rhombohedral siderite containing a few 

 tetartohedral particles. 



Rhodochrosite, according to Tschermak (Min.-Petr., p. 

 116), gave asymmetrical figures which does not accord in 

 the least with the results obtained by the writer (see pho- 

 tographs). 



While the figures produced on the various carbonates 

 differ more or less, as also obtained by the writer, 

 Tschermak in his investigation observed a greater sim- 

 ilarity between calcite and sodium nitrate and between 

 magnesite and siderite. 



Otto Meyer 3 also investigated Iceland spar, obtaining 

 well-defined figures with HC1 and acetic acid. The HC1 

 figures are very similar to those described by Baumhauer 

 but the acetic acid forms are five-sided, with the sharp 

 angle turned upward; a mixture of the two acids gave 

 different results, some of the figures being semicircular, 

 others slightly oval with four and five bounding faces. 



J. S. Pratt 4 observed etch figures on the base of Mon- 

 tana sapphires. The figures are very perfect, and 

 although they show different forms they reveal the dihex- 

 agonal alternating symmetry. The most common form is 

 the simple triangular depression, bounded by three 

 planes, the intersections of wdiich with the base are 

 straight well-defined lines. The rhombohedral depres- 

 sions were measured and the faces calculated as (10T7). 



Occasionally these triangular forms possess a fourth 

 face of varying size, lying at the bottom; the larger fig- 



2 Beriehte der deutsch. Chem. Ges., 1872, p. 857. 



3 Jb. Min., 1, 74, 1883. 



4 This Journal, 4, 424, 1897. 



