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Ch. 3: Turquoise

Ch. 3: Turquoise Page of 364 Ch. 3: Turquoise Text size:minus plus Restore normal size   Mail page  Print this page
58                             GEMS AND PRECIOUS STONES IN THE
hands of Professor Clarke, chief chemist of the United States Geological Survey, and are now deposited in the United States National Museum Collection.
This mineral varies in color from a fine sky-blue through many shades of bluish-green and apple-green to dark-green, showing no blue whatever. The dark-green nodules pass to white at the center, sometimes resembling in structure certain varieties of malachite. Many of the specimens obtained by Major Powell, which are seamed or streaked by limonite, Professor Clarke suggests have been derived from the accom­panying pyrite ; and the latter mineral is occasionally found, bright and unaltered, enclosed completely in masses of clear blue turquoise. Three samples, selected as representing as nearly as possible the most definite types of the mineral, may be briefly described as, A. Bright blue, faintly translucent in thin splinters. B. Pale blue with a slight greenish cast, opaque and earthy in lustre, and having a specific gravity of 2*805. C. Dark green in color and opaque. These were analyzed, with the fol­lowing results :
In Professor Silliman's paper there is reported 3*81 of copper, which corresponds to 478 of copper monoxide. On account of the value of this gem, attempts have been made to color it by artificial means. The discovery of this deception was made by the writer, who saw numerous parcels of turquoise sent to New York from New Mexico, and among them several small lots with an exceptionally fine color for American specimens. This color did not appear to be natural, although the stones
1 Analysis A was not completed, as material enough could not be obtained without the destruction of two valuable specimens. The silica in it was due to traces of admixed rock from which the material could not be perfectly freed. C, however, was free from rock, and the silica in it must be otherwise accounted for.
Ch. 3: Turquoise Page of 364 Ch. 3: Turquoise
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