L. V. Pirsson — Fowlerite variety of Rhodonite. 487 



m, 110. Often instead of having a nearly equal breadth and 

 thickness, there is a greater development of the basal planes, 

 giving rise to flat, tabular forms. One of these is shown in 

 Fig. 4. This particular crystal was also characterized by the 



pyramid — 4'. For reasons already stated, the smallest crystals 

 could not be measured or figured with any exactness, to show 

 their more complex forms. In some the rounding off of the 

 planes is so great that they are nearly spherical in shape. 



The cleavage is prismatic, perfect, like the normal type of 

 rhodonite ; the following were measured 001 -^ 110 (cleavage) 

 86° 47', calc. 86° 4.1'; 110^110, (cleavage) ^(cleavage) 92° 

 39f', calc. 92° 49^; 001 ^ 110 (cleavage), 70°, calc. 68° 25'. 



In the endeavor to ascertain whether this variety differed in 

 any degree, in its optical orientation from the normal type, 

 great difficulty was found in making thin sections. It was 

 nearly impossible to grind such a hard brittle material com- 

 pletely filled with cleavage cracks to any satisfactory degree of 

 thinness. After considerable search, however, a small trans- 

 parent tabular crystal was found which could be used for an 

 oriented basal section and on this the angle of extinction was 

 about 54° from the edge of the prism 110, in the acute angle 

 110/\110. Flink gives 54° 26' and from this it is inferred 

 that there is little or no difference in the position of the axes 

 of elasticity. 



For the chemical analysis, only such small transparent or 

 translucent crystals or crystal fragments were chosen, that in 

 transmitted light, by the aid of a lens were seen to be pure 

 and free from inclusions and from any adherent material. 

 They were treated with weak hydrochloric acid to remove any 

 adhering calcite, washed and dried and their specific gravity 

 carefully taken with a pygnometer at about 65° F. It was 

 3*674. The material was then dried, powdered, dried at 100° 

 C. and subjected to analysis. A synopsis of the method used 

 is as follows : Silica was separated by the usual sodium car- 

 bonate fusion. Iron separated as a basic acetate and tested for 

 silica. Zinc precipitated in the filtrate as a sulphide and 

 determined by changing to a carbonate. The manganese was 

 then separated from the lime and magnesia by bromine and 



