Dihexagonal Alternating Type. 203 



ures often reveal small triangular pits implanted in them, 

 producing- a figure Avithin a figure, with the same shape 

 and orientation. In many cases the outer contour is 

 curved, this variety of figure usually being the deeper one. 

 Bauer 5 also observed similar figures upon the base of 

 Burma rubies. 



Artificial Etchings. 



The writer in his investigation of the etch figures of 

 this type selected five of the isomorphous carbonates, cal- 

 cite, magnesite, siderite, rhodochrosite and smithsonite. 

 These were etched and studied with a view to comparing 

 and contrasting the solubilities and etchings produced 

 under similar conditions. Unfortunately calcite is the 

 only one of the five minerals which offered a variety of 

 forms for study. Consequently the work done in this 

 connection deals principally with the behavior of the 

 unit rhombohedrons when acted upon by acids, the other 

 forms being so very rare, or so corroded, as to be useless 

 for etching. 



The calcite crystals used were taken from beautiful 

 crystal clusters collected at Cumberland, England; the 

 crystals are very bright, and transparent, varying from 

 5mm. to nearly an inch in length; they are attached by 

 the base, and terminate by either r (1011) or e (1101) and 

 the scalenohedron v (2131) ; two prisms, 1010 and 1130, 

 occur, the 1010 form being much the larger; 1120 is 

 deeply grooved parallel to its intersection with the scalen- 

 ohedron. These crystals were used for etching the unit 

 prism and the scalenohedron principally, as these forms 

 were more perfect. For the base and second-order prism, 

 small transparent crystals from Patterdale, Cumberland, 

 England were used, which showed only the two forms 

 mentioned. A cleavage piece of Iceland spar gave the 

 etch figures on the unit rhombohedron. The remaining 

 two forms, the hexagonal pyramid and the dihexagonal 

 prism, due to rarity, could not be obtained and for that 

 reason were necessarily omitted in this work. Cleavage 

 pieces of a very clear magnesite, locally unknown, were 

 found very desirable for etching. 



Siderate crystals were not so easily obtained, although 

 several fine specimens from the museum were examined. 



5 Jb. Min., p. 209, 1896. 



