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An experimental evaluation of mineral‐specific comminution
Author(s) -
Cintala Mark J.,
Hörz Friedrich
Publication year - 1992
Publication title -
meteoritics
Language(s) - English
Resource type - Journals
eISSN - 1945-5100
pISSN - 0026-1114
DOI - 10.1111/j.1945-5100.1992.tb00221.x
Subject(s) - regolith , comminution , pyroxene , feldspar , olivine , mineral , geology , mafic , quartz , geochemistry , mineralogy , gabbro , detritus , astrobiology , materials science , igneous rock , metallurgy , physics , paleontology
— Early “regolith‐evolution” experiments using fragmental, polycrystalline gabbro targets displayed mineral‐specific comminution trends, with feldspar being significantly fractionated into the finest grain sizes. Since planetary regoliths are similar mixtures of lithic and monomineralic detritus, the comminution of monomineralic grains is important in understanding the evolution of such regoliths. Particulate targets of monomineralic feldspar, olivine, pyroxene, and quartz therefore were subjected to at least 25 impacts each to complement the previous gabbro‐based investigations. Stainless‐steel projectiles 3.18 mm in diameter were launched at the targets at nominal velocities of 1.4 km s −1 , depositing an average of about 2.6 × 10 6 ergs per g of target per impact. The quartz and feldspar comminuted most readily, while olivine and pyroxene were the most resistant. In addition, the feldspar and quartz were virtually indistinguishable in terms of any measure of comminution used here. The behavior of the olivine differed somewhat from that of the pyroxene, but the variation between these two minerals was much less than the difference between them and the tectosilicates. The apparent energy required to create new surfaces through comminution was about a factor of two higher for the mafic minerals. Densities of pre‐existing cracks and other crystal defects depend on sample preparation techniques, among other things, and appear to play a notable role in the early evolution of these “regoliths.” It is probable that the history of a particular regolith's parent rocks will exert a comparable influence on the early stages of evolution of a planetary regolith. The trends for the individual targets in these monomineralic series duplicated those exhibited by the gabbro charges, leading to the general conclusion that mineral‐specific comminution will occur during repetitive impact of planetary surfaces, whether they comprise freshly excavated, large blocks, or highly comminuted, clastic fines containing substantial fractions of monomineralic debris. This mineral‐specific behavior will cause small grain sizes in planetary regoliths to be substantially fractionated relative to coarse regolith components, and especially relative to their source rocks.