W. IT. Hobbs — Lime- and- Alumina-bearing Talc. 405 



are simple pentagonal dodecahedrons of pyrite about a milli- 

 meter in diameter, which are colored brown from superficial 

 alteration to limonite. On lines evidently corresponding to 

 fracture planes in the rock, is developed a talcose mineral. 

 Other fracture lines are occupied by vein dolomite, one cleav- 

 age surface extending several centimeters. In one of the 

 specimens the talcose mineral has a deep rose color, somewhat 

 deeper than that of the margarite from Chester, Mass. In 

 the other specimen the color is white or nearly so, but Mr. 

 Adam informed me that when found it had the same rose hue 

 as the first mentioned specimen. The rose color has faded 

 through exposure to the light, resembling in this respect rose 

 quartz. 



The scales of this talcose mineral lie with entire lack of any 

 regular orientation, completely filling the fissure. Scales one- 

 half a centimeter across can be obtained having roughly hexag- 

 onal outlines, but which are too poor for accurate measure- 

 ment. They are very flexible but entirely inelastic. They 

 have the softness and unctuous feel of ordinary talc. After 

 treatment with dilute hydrochloric acid to remove any pos- 

 sible trace of calcite, nearly a gram of the material gave a 

 specific gravity of 2 -86 by determination with the pyknometer. 

 In the closed tube the powdered mineral yields considerable 

 water. Ignited before the blowpipe it resembles talc in exfoli- 

 ating, whitening and glowing intensely. It is, however, much 

 more fusible, falling below 5 in v. Kobell's scale. It is also 

 more readily decomposable than common talc. When digested 

 for only a short time in hydrochloric acid, the solution yields a 

 considerable amount of alumina and calcium. 



Between crossed nicols in convergent light, scales of the 

 mineral show a negative bisectrix perpendicular to the plane 

 of cleavage. The optical angle, which is very small, lies in 

 the plane perpendicular to one of the bounding planes, and 

 also perpendicular to a side of the hexagon of the percussion 

 figure. It therefore corresponds to a mica of the first class. 

 2E was measured in sodium light as 15^-°. 



I am indebted to my friend, Mr. Louis Kahlenberg of the 

 University of Wisconsin, for a chemical analysis of this mineral. 

 His results are given below in the first column. In the last 

 column is given the theoretical composition of ordinary talc : 



