Glass-Coated Lunar Rock Fragments

Abstract

Glass-coated rocks commonly occur as isolated fragments in the lunar regolith and as clasts in friable, feldspathic breccias. Three main types of coatings are: (1) veneers with sharp contacts between the glass and the coated rock; (2) selvages with gradational boundaries between the glass and the coated rock; and (3) grooved coatings on slickensided surfaces. Textures and modes of occurrence of the glass indicate that fusion by shock heating, shearing, fracturing, emplacement of melt, and ejection of fragments were part of a continuous, complex process of impact cratering. A descriptive model is presented to illustrate the sequence and position in a growing crater of formation of the different types of coatings, and possible relationships between the coatings and the coated fragments. Injection of molten material and fusion along subfloor fractures followed by cataclastic flow may form glass-coated clasts in certain feldspathic breccias without ejection from the crater.