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Volume 17, pages 492-493, 1932
UNUSUAL FELDSPAR CRYSTALS AT MONETA, VIRGINIA
JAMES H. BENN,* United States National Museum.
The Seaboard Feldspar mine, near Moneta, Nelson County, Virginia, has produced some unusual crystals of feldspar. This occurrence is exceptionally interesting due to the frequency of crystals remarkable for their size and sharpness of form. The advisability of securing one of these for exhibition was brought to the attention of the United States National Museum by Dr. W. T. Schaller, who, while visiting the locality saw a huge crystal which had been removed from the mine. Museum authorities then communicated with the Seaboard Feldspar Company in Baltimore, who offered to present the crystal provided the Museum assumed the responsibility of transportation. Fearing damage if shipment were made by freight or express, the writer was detailed to superintend the removal of the crystal and its transportation to Washington by truck.
The workings of the Company are located about 250 miles southwest of Washington and a short distance from Moneta, Va., and consist of an open pit approximately 500 feet long, 200 feet wide, and 100 feet deep, situated on the crest of a hill. In character the formation is a pegmatite occurring in the metamorphosed rocks of the Piedmont. The mine is approached most conveniently via Bedford, Va., preferably by auto. About a mile from Moneta, the road comes to a T-shaped junction; following the left branch for some 300 or 400 yards, a road to the right is encountered, which eventually leads to the site of the workings. Piles of debris mark its location, visible to the right about a mile from the point where the last mentioned road is entered.
The large crystal of orthoclase proved fully equal to expectations, weighing approximately 800 pounds and measuring about 2 feet high and 3 feet long. It was transported safely and is now on exhibition in the hall of economic geology (Nat. Mus. No. 96,543).
A smaller and more perfect crystal, weighing 62 pounds and measuring 16 by 9½ X6 inches, was secured at the mine from Mr. B. O. Harris (Nat. Mus. No. 96,561). Measurement with a hand goniometer resulted in the following determinations:
The crystal habit is very much elongated, parallel to the a axis, with c face one and one-half times as wide as b, or nearly equal in size. In general the habit of feldspar from this locality tends toward an elgonated form. One crystal reported from the mine had a six-inch base and was elongated to six feet. The superintendent of the mine described it as resembling the Washington monument. The specimen, after being held at the mine for some time, suddenly disappeared; it is thought to have been stolen.
Associated minerals found occurring with the feldspar are quartz (mostly massive), muscovite, pyrite, limonite, zoisite, thulite, and spessartite, of which the writer was permitted to collect samples. Among several of the larger feldspar crystals observed in the walls of the mine was one measuring approximately 3 feet wide and 6 feet high. All of those seen rested in place vertical to the bottom of the pit. Estimates show that more than 30,000 tons of commercial feldspar have been removed since 1925.
* Published by permission of the Secretary, Smithsonian Institution.