Precious Gem stones production in 1916 Page 72



	GEMS AND PRECIOUS STONES. 893

	lel structures which are oriented with reference to crystallographic directions in the diamond. Striations and well-defined etch figures are absent. DUMORTIERITE. Two new localities of the hydroborosilicate of aluminum, dumor-tierite, have been recently found. One is in New Mexico and the other in Nevada. This mineral, until recently considered very rare, has now been found in seven States—New York, Colorado, Washington, New Mexico, Nevada, Arizona, and California, in the last four of which it occurs in abundance. The New Mexico locality is about 100 miles west of El Paso, 12 miles northwest of Columbus, in the Tres Hermanas Mountains, southern New Mexico. This-deposit of dumortierite has been referred to in the press as lapis lazuli. The ledge containing dumortierite is said to be several feet wide with an outcrop of over 1,000 feet. Many boulders with seams of the mineral lie on the ground. A sample sent to the Geological Survey by W. A. Casler, of Deming, N. Mex., shows a quartz rock, in part sericitized, with narrow seams a quarter of an inch wide and the same distance apart, composed of spherulites of blue dumortierite with smaller amounts of colorless spherulites of similar structure, which are formed of mica. In places the mica spherulites appear to have been derived from the alteration of the dumortierite; at other places the two minerals seem to be intergrowths. If large pieces suitable for cutting and polishing are obtainable, the occurrence should yield a striking ornamental stone, for the narrow seams of bright blue dumortierite in the white rock afford a very attractive contrast. Well-selected and cut pieces, with a narrow band of the dumortierite, might also yield cut stones of value in jewelry. Nevada also has an extensive deposit of dumortierite, and Adolph Knopf, of the United States Geological Survey, has kindly furnished the following note on the occurrence: Dumortierite occurs in great abundance in the Rochester district, in Humboldt County, Nev. On the west flank of Lincoln Hill in this district there is a large area of Triassic rhyolites that are cut by innumerable veinlets composed of dumortierite and quartz. The rock inclosed between the veinlets has been highly altered to an aggregate consisting of andalusite, quartz, dumortierite, and white mica. The dumortierite of this Nevada occurrence is prevailingly lavender and pink in color, the blue, usually thought to be characteristic of dumortierite, being very rare. The veinlets, so far as is now known, range from a friction of an inch to 6 inches in thickness. The thicker veinlets consist more largely of quartz than the smaller ones, and some of this quartz is noteworthy because of its fine rose color. Between this rose-colored quartz and the pure pink dumortierite all stages of gradation due to intergrowth can be seen, and under the microscope the clear rose-colored quartz is found to inclose numerous hair-like fibers of dumortierite, to which the color of this new variety of rose-colored quartz is due. By careful prospecting of the area in which the dumortierite occurs it is possible, though by no means certain, that rose-colored quartz of a quality suitable for polishing as a precious stone may be found. GARNET. Small quantities of garnets are produced each year in several of the States. In 1917 the mineral of gem quality was obtained from Arizona, California, Colorado, Idaho, Maine, Montana, New York,