The component and isotopic composition of the rare gases in beryls, cogenetic pegmatite minerals, and metamorphic cordierites has been measured. Beryls contain large amouonts of excess radiogenic gases and significant amounts of nonradiogenic gases. Beryls contain the most pristine samples of the rare gases in pegmatite volatile phases but have imposed significant elemental fractionations duriing crystallization. Both the excess radiogenic and nonradiogenic components are progressively depleted in the heavy gases relative to the light gases. Other pegmetite minerals contain rare gases with mucch smaller excess radiogenic components and apparently did not sample the same source as did the beryls. The other minerals exhibit varying but mineral-specific fracctionation patterns for the nonradiogenic gases. In addition, ordierites show a strong, consistent fractionation of both gas components. The fractionation pattern is significantly different from that found in beryls and is characterized by an enrichment of Xe relative to the Ar, though both gases are depleted relative to He. The cyclosilicates can serve as probes of the rare gases present in the volatile phases when the cyclosilicates crystallized. Thed cyclosilicates contain a record of the rare gases present in geologically interesting environments over a wide range of time and physical conditions.