Bulletin of the United States Geological Survey--Corundum and Its Occurrence and Distribution in the United States (A Revised and Enlarged Edition of Bulletin ) . i.|,f 3een found that have cut good gems. Stones approaching a red orjlue color are, however, extremely rare. There are still a great many sapi)hircs in the gravels that have notbeen worked, but on account of their color it is rather doubtfulwhether under the most favorable conditions it wull i)ay to mine cr3^stals from all these l)ars show the same development, andare prismatic in habit. The prism, a (1120), is always
Bulletin of the United States Geological Survey--Corundum and Its Occurrence and Distribution in the United States (A Revised and Enlarged Edition of Bulletin ) . i.|,f 3een found that have cut good gems. Stones approaching a red orjlue color are, however, extremely rare. There are still a great many sapi)hircs in the gravels that have notbeen worked, but on account of their color it is rather doubtfulwhether under the most favorable conditions it wull i)ay to mine cr3^stals from all these l)ars show the same development, andare prismatic in habit. The prism, a (1120), is always present, andis usually in combination with the base, v (0001), and the unit rhom-bohedron, /• (1011), as represented in fig. 16, A. Some of tlie crystalsave the prism very short and the rhombohedroii is Avanting, givingthe crystal a very tabular appearance (fig. 10, B). A pyramid of thelecond order, n (2243), was observed on some of the crystals in addi-ion to the base and unit rhombohedroii, and is represented in fig.[6, crystals are usually rough and more or less striated, so that noleasurement could be made upon the reflecting goniometer, but suf- (p. A. B. a. Fig. 16.—Sapphire crystals from Missouri River bars, Montana. ficiently accurate measurements could be obtained with the contact - goniometer to identify the faces. The largest crystal that has been observed from an}^ of these bars ,jl jwas one from Eldorado Bar that was nearly an inch long and three- 1,1 pighths of an inch in diameter. f(i] A repeated growth was observed on some of these crystals, but not|in the variety of forms seen in the Cowee rubies (p. 101) and the Togo i,(l(iGulch sapphires (p. 113). Only one form of grow^th was observed. jJrepresented in fig. 16, A, which is a combination of the unit rhombo- ,j|hedron and the base. Since the discovery and mining of sapphires from the MissouriRiver bars sapphires have been found at three other localities in Mon-tana—at Kock Creek, Granite County; at
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