Abstract

Vugs in basalt from Hat Creek Valley, California are lined with subhedral to euhedral crystals of plagioclase, pyroxene, olivine and magnetite. The olivines reveal two surface features: rows of platelets (hematite?) and thin films coating the entire olivine crystal surfaces. The presumed hematite platelets are perpendicular to the direction of the rows and are parallel to the (100) plane to the underlying olivine. The rows lie in the (001) plane. It is probable that both the platelets and the thin films are the result of vapor condensation. There may be a structural control between the olivine crystals and the hematite platelets that cause their arrangement parallel to the (100) plane of the olivines and the arrangement of the rows in the (001) plane. Structural control could also explain the absence of these features (except occasionally on plagioclase) on other vug minerals.

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