556 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.53. 



to composition. They may possibly represent some form of iron 

 oxide or manganese oxide or both. 



The evidence gained from microscopic study of the thin sections 

 strongly indicates that the color of the two varieties of quartz can 

 not be ascribed to microscopically visible inclusions, since in general 

 character and abundance the inclusions were apparently not different 

 from those frequently found in ordinary colorless quartz. 



HEATING TESTS. 



The color of many dispersely colored minerals has been shown to 

 be very sensitive to high temperatures, and in some cases even to 

 sunlight. Such minerals include halite, fluorite, amethyst, smoky 

 quartz, topaz, zircon, tourmaUne, etc. To this list should be added 

 rose quartz and green feldspar (amazon stone). Upon testing it is 

 very likely that other minerals will be shown to decolorize on heating. 



Previous work. — Jn 1883 Becquerel ^ showed that the color of 

 the decolorized fluorite and halite was restored on exposure to the 

 cathode rays. More recently Berthelot ^ (1906) and Simon ^ (1908) 

 showed that the color of some of the decolorized minerals is restored 

 on exposure to radium rays, while that of others was not restored 

 by these radiations. From these experiments the conclusion was 

 reached that for the minerals studied (zircon, amethyst, smoky 

 quartz, red tourmaline, and Brazilian topaz by Simon), the color 

 was due to inorganic and not to organic compounds, since exposure 

 to radium rays restored the minerals to their original condition. 

 Berthelot concluded that the coloring substance of smoky quartz, 

 green fluorite, and emerald was organic, since the color of these 

 minerals was not restored on exposure to radium rays after being 

 decolorized by heating. Simon, however, was successful in restoring 

 the color of smoky quartz after it was destroyed by heat, hence 

 excepted to Berthelot's conclusion regarding the nature of the 

 coloring substance of this mineral. 



The action of Roentgen, cathode, and radium r&js on minerals has 

 been extensively investigated b}'^ Kunz and Baskerville.* 



Worlc of the writers. — Heating tests were carried out by the writers 

 on fairly large size fragments chipped from hand specimens of 

 amethyst, rose quartz, blue quartz, green feldspar (amazon stone), 

 and green and purple fluorite. The tests were made under uniform 

 conditions in a closed platinum crucible heated in each case for 10 



« Compt. Rend., 1883, vol. 101, p. 205. 



» Idem, 1906, vol. 143, p. 477. 



» Xeues Jahrb. f. Min. etc., 1908, vol. 26, pp. 249-295. Seo translation by Edgar T. Wherry, Mineral Col- 

 lector, 1908, vol. 15, pp. 165-168, 177-182. Contains numerous references to the literature of the color oX 

 minerals. 



< Science, 1903, vol. 18, p. 769; Mineral Collector, 1904, vol. 11, pp. 82-86. See Lockhart, Araer. Jouni. 

 Sci., 1905, vol. 8, p. 95, on luminescence; and Miethe, Ann. des Phys., 1906, vol. 19, p. 633, on the color 

 Changes in precious stones produced by radium preparations. 



