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Ch. 4: Topaz and Tourmaline (Rubellite, Indicolite and Achroite)

Ch. 4: Topaz and Tourmaline (Rubellite, Indicolite and Achroite) Page of 364 Ch. 4: Topaz and Tourmaline (Rubellite, Indicolite and Achroite) Text size:minus plus Restore normal size   Mail page  Print this page
68                             GEMS AND PRECIOUS STONES IN THE
to beautiful topazes occurring in the lithophyses of rhyolite, which is the first noted occurrence of this gem in an eruptive rock.' This rock was, however, first identified by Whitman Cross, and its exact locality is directly opposite Nathrop, Col., on a ridge a quarter of a mile in length and about 200 feet in height. Here the topaz is found in more or less rounded cavities, partially filled by its curved walls, which by concentric arrangement and an over­lapping often produce a roselike form. These cavities are often lined with minute, glassy quartz crystals, and on them are found the topazes, which are prismatic in form, and, being attached to
TOPAZ
the sides of the cavities in all positions, are often found doubly terminated. The crystals are from i to (rarely) i inch in length and i to i inch across the prism. In color they are generally transparent and flawless, and are either colorless, pale-blue, or distinctly sherry-colored. A similar occurrence is noted by Mr. Cross, in the nevadite of Chalk Mountain, but the crystals are somewhat smaller. Chalk Mountain is situated at the junc­ture of Lake Eagle and Summit Counties in Colorado.1 Many fine large topaz crystals have been found at Crystal Park, near Pike's Peak, El Paso County, Col. Three crystals from this lo-
1 Report on the Development of the Resources of Colorado, p. 36, 1881-1882. ' Am. J. Sci. III., Vol. 27, p. 94, Feb., 1884.
Ch. 4: Topaz and Tourmaline (Rubellite, Indicolite and Achroite) Page of 364 Ch. 4: Topaz and Tourmaline (Rubellite, Indicolite and Achroite)
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