Precious Gem stones production in 1908 Page 33



	810	MINERAL RESOURCES.

	feet above sea, and one-half of a mile south of the top of Mount Antero, on the west slope of Mount Antero, and on smaller peaks to the east of it. Former glaciers have left their marks in the region by cirques, moraines, and lakelets in the surrounding valleys. The gem locality is reached from the little town of Alpine, or from Fisher station, on the narrow-gage branch of the Colorado and Southern Railroad between Buena vista and Gunnison. From Alpine the distance is about 8 miles and the climb about 5,000 feet. Over half of the trip can be made on burro or mule back. The mass of Mount Antero and White Mountain is composed of quartz monzonite with local variations. Along the divide half a mile southwest of White Mountain an abrupt change of character to more basic rock is indicated by an area of dark-brown soil on Calico Mountain. The talus slopes and angular gravel-covered surfaces of Mount Antero and White Mountain appear light gray and frost-white in contrast to Calico Mountain. On parts of White Mountain, especially near the beryl deposits, the rock is muscovite granite composed of orthoclase with microperthite intergrowths, oligoclase, quartz, muscovite, and a little biotite. Magnetite, apatite, and zircon are present as accessories. The beryl, quartz, phenacite, and topaz crystals occur in micro-litic cavities and pockets in the granite and granitic phases of the quartz monzonite. The pockets occur in streaks or are isolated and occupy no definite arrangement with respect to each other. The crystallization along the streaks and around the miarolitic cavities is coarse, and the rock may be called pegmatite. One streak-or vein of pegmatite with its gem-bearing pockets is 15 inches thick where exposed in a pit. This streak can t>e traced for some distance in a northeast direction across the ridge near the top of White Mountain by loose beryl and quartz crystals in the angular gravel soil formed by the disintegration of the rock and in blocks of the granite lying on the surface. As exposed in the pit the vein consists of pegmatite, much crystallized clear and smoky quartz penetrated by beryl crystals, crystals of phenacite, muscovite mica, feldspar, violet and green-colored fluorite, etc. Crystals of beryl and quartz occur scattered along the top of the ridge from the summit of White Mountain for about 200 yards to the southwest. In places many crystals may be found loose in the gravel, indicating the position or a gem pocket. With the exception of smoky and clear quartz, beryl is the most abundant specimen and gem mineral found at the Mount Antero locality. The beryl occurs in transparent clear crystals from small size to those measuring 2 centimeters in diameter and 6 centimeters in length. Many of the crystals are badly etched or corroded, especially on the ends projecting into cavities. The color of the beryls varies from clear light blue to pale and deep aquamarine green. Blue beryl is very plentiful "frozen" in the rock, either in the granite, pegmatite, or quartz. Much of the frozen beryl is badly checked and flawed. That from the cavities is generally clear and of gem quality. The other minerals—phenacite, topaz, and fluorite—are closely associated with the quartz and beryl, and often attached to them. Phenacite crystals attain the size of the beryl and are generally colorless. S. L. Penfield^a has described the beryl, bertrandite, and phenacite from Mount Antero. He discussed the etching of the a Beryllium minerals from Colorado: Am. Jour. Scl., 3d Ser., vol. 40, 1890, pp 489-491.