The Black Cloud pegmatite, which is exposed 800 feet north of U. S. Highway 24, 2.3 miles west of Divide in Teller County, Colorado, was studied in June 1957 and June 1958. Laboratory studies were completed between September 1958 and May 1959. Both field and laboratory work were supported by a grant from the Michigan Memorial-Phoenix Project Fund, Project 150. This study is part of a continuing investigation of the pegmatites of the South Platte-Pikes Peak area of Colorado, to which field work during the last three summers has been devoted (Heinrich, 1958), and represents an extension of a previous reconnaissance study of rare-earth pegmatites in Colorado (Heinrich, 1948).

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