458 Hillebrand, Ticrner and Clarke — Roscoelite. 



Prof. Hanks* states that roscoelite was also found in Sec. 31, 

 T. 11 N. Range 10 E, two miles from the Stockslager mine. 

 This appears to be the Thompson Hill locality of Kimble, to 

 whom, indeed, Prof. Hanks was probably indebted for his 

 information. Hanks states that the roscoelite was found here 

 in the bed rock of Big Red ravine in a dark-colored micaceous 

 rock in small seams of quartz with calcite and gold. 



The roscoelite from California shows a tendency to crystal- 

 lize in little rosettes, so that individual scales of any size with 

 the same optical orientation throughout are difficult to obtain. 

 Some scales gave with convergent light a nearly uniaxial black 

 cross, the hyperbolas opening but slightly on rotation, indicat- 

 ing a small axial angle. Like all other micas it is optically 

 negative. The pleochroism as seen in thin foils is, c and 6 clove 

 brown to greenish yellow brown, a light greenish yellow. In 

 the scales of the powder analyzed no rutile needles or other 

 inclusions were detected, but in the center of a rosette of ros- 

 coelite scales were found dark grains with a metallic luster. 

 These grains are of sufficient size to have fallen with the heavy 

 minerals during the process of separation with the Thoulet 

 solution, and it is not likely that any of them have been 

 included in the powder analyzed, although they were noted in 

 the impure material before it had undergone the final separa- 

 tion. The grains show no crystal form and were not deter- 

 mined. 



* Loco citato, p. 263. 



