The Brown Derby group of pegmatites and especially the Brown Derby No. 1 pegmatite on the east side of Quartz Creek Valley in Gunnison County, Colorado, are famous for the exceptional development of the variety of pegmatitic minerals that they contain, ever since the discovery in them of lepidolite (Eckel, 1933). Minerals from this dike and its parent granite also have been used extensively for age determinations (e.g., Aldrich et al., 1956). The geology of the dikes and of the district has been thoroughly investigated (Hanley et al., 1950; Staatz and Trites, 1955), and many of the minerals have been studied in detail: microlite (Eckel and Lovering, 1935); tourmalines (Staatz et al., 1955); columbite (Heinrich and Giardini, 1957); garnet (Jaffe, 1951), the micas, especially the lepidolites (Heinrich et al., 1960B); and monazite (Heinrich et al., 1960A). A list of the minerals identified with certainty from the Brown Derby group is given in Table 1.

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