Merrillite, a whitlockite-group mineral in Yamato-75 chondrites

• Main Authors: Yasunori Miura, Yukio Matsumoto
• Format: Report
• Language: English
• Published: Department of Mineralogical Sciences and Geology, Faculty of Science, Yamaguchi University 1982
• Subjects: Yamato; Memoirs of National Institute of Polar Research; Polar Research
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=1383; http://id.nii.ac.jp/1291/00001383/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=1383&item_no=1&attribute_id=18&file_no=1

Various sizes of merrillite of whitlockite-group minerals (from 20 to 750μm in length) occur as irregularly-shaped grains in Yamato-75 chondrites. The merrillite in the Yamato-75135,93 chondrite coexists with olivine, pyroxene, plagioclase, chromite and/or metal phases in the matrix. This calcium magnesium phosphate with small amounts of Na and Fe shows compositional variation in grain to grain larger than that in an H6 chondrite, but smaller than that of lunar rocks. Electron microprobe analysis and textural evidence indicate that the merrillite was initially present as molten droplets, interstitial to olivine, and coexisted with orthopyroxene and plagioclase, and/or to chromite clusters at the stage of matrixformation induced by multiple-impact metamorphic events.