Impact comminution of glasses: Implications for lunar regolith evolution

Glasses are important parts of every lunar regolith sample, whether in the form of indigenous melts such as mesostasis or pyroclastics, or as quenched impact melts. The modal proportions of agglutinitic impact melts alone can exceed 50 percent for some mature regoliths, and glasses are commonly the most dominant single component of lunar soils. They therefore participate in and possibly affect all evolutionary processes to which regoliths are subjected, such as comminution and attendant chemical fractionation as a function of grain size, the retention of solar-wind products, the production of superparamagnetic iron, and others. Because they are such an integral part of lunar regoliths, a more complete understanding of regolith evolution must include the role played by these vitreous components. This contribution examines the comminution behavior of a variety of glasses and a fine-grained basalt under conditions of repetitive impact, and compares this behavior to those of crystalline components, such as lithic fragments and major rock-forming minerals.