NO. 3 



SMITHSONIAN EXPLORATIONS, I915 



21 



have been noted on the specimens, although cleavage planes, beveling the 

 edges of the surface form, are visible here and there. The faces of the nega- 

 tive rhombohedron are not smooth nor simple, but are built up of a series of 

 innumerable smaller faces, belonging to individuals in approximate parallel 

 position, though with enough divergence to cause the curvature of the faces ; 

 while at the thin edges of the crystals the individuals are still more distinctly 



Fig. 30. — Calcite rosette showing somewhat different structure from that of 

 Fig. 29. Dr. Edgar T. Wherry, of the United States National Museum, 

 explains their origin as due to starting of crystallization at numerous closely 

 crowded points, the crystals being perhaps at the start quite parallel, but as 

 they grew crowding one another out of parallelism, although not enough to 

 prevent approximately equal growth of every individual. He states that this 

 type of crystallization of the mineral calcite is comparatively rare. Photo- 

 graph by Mr. T. W. Smillie, U. S. National Museum. 



separated, so that the effect is that of superposed layers of curved sheets, 

 resembling the petals of the rose to such an extent that the first word to 

 describe them which suggests itself is " rosette." 



