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GEMS AND PRECIOUS STONES.
1053
the Natural History Museum, New York, has furnished information concerning two other fine crystals placed in the Morgan collection. One of these is 9 inches high, 5 inches wide, and about three-fourths of an inch thick. It shows a fine deep suffused lilac coloration when viewed parallel to the vertical axis or length. The other crystal is 7 inches high, 5 inches wide, and three-fourths of an inch thick. Both arc of gem quality and are free of all matrix and associations. They are strongly striated as usual, but have perfect terminations.
TOPAZ.
TEXAS.
The following notes on the occurrence of topaz in Mason County, Tex., have been abstracted in great part from a description by II. Con­rad Meyer.1 Topaz has been found at two places near Streeter and near Katemcy, respectively. Streeter is about 8 miles due west and Katemcy about 12 miles north of Mason, the county seat. This dis­covery of topaz was made in 1904 by the late R. L. Parker, of Streeter. Mr. Parker was attracted by the unusual weight of a supposed quartz crystal he had found in the bed of a stream on the land of Sam Await, near Streeter. He submitted it to a mineralogist, who pronounced it topaz. A careful search revealed the original matrix of the topaz, but the first work was confined chiefly to ' 'dry washing" of the alluvial deposits. The topaz thus obtained consisted of waterworn crystals, with frosty-appearing surfaces. These were found to contain clear, limpid interiors when broken. Regular development of the topaz vein was not undertaken until 1908. Only a limited amount of work has been done on any of the deposits since 1910. In all a dozen or more prospect holes have been made at this locality.
Meyer refers to the report on the rare-earth minerals of Llano County, by F. L. Hess,2 for a general description of the geology of the region. Hess speaks of the Llano region as an island of pre-Cambrian rocks intruded by plutonics and surrounded by an irregular zone of Cambrian and other Paleozoic rocks. The principal plutonic rocks are granites, which present several phases. An important variety, and one which Meyer mentions as the country rock at the topaz localities, is a rather coarse-grained red granite. The general geology of the Llano region, including a more complete description of this granite, has been given by Sidney Paige.3
The topaz occurs in pegmatite, but with different associations at the two localities. At the locality near Streeter the crystals are found in vugs partly filled with clay and associated with microcline feldspar, biotite, tourmaline, smoky quartz, and albite. The micro­cline is flesh-colored and occurs in large crystals. Smoky quartz, in many places intergrown with topaz, and biotite are quite abundant. The albite is found in fan-shaped laminated aggregates and is the clevelandite variety. Black tourmaline is sparingly present in small needle-like crystals. Some 200 pounds of good topaz crystals have been obtained. Besides the clear, colorless crystals, a small number of beautiful light-blue crystals, rivaling those of Siberia, have been
1 Topaz and stream tin in Mason County, Tex.: Eng. and Min. Jour., Mar. 8,1913, pp. 511-512.
• Bull. U. S. Geol. Survey No. 340,1908, pp. 286-294.
' Llano-Burnet [olio (No. 183), Geol. Atlas U. S., U. S. Geol. Survey, 1912.