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Claire L. McLeod 1, Mark. P. S. Krekeler (August 2017). «Sources of Extraterrestrial Rare Earth Elements: To the Moon and Beyond». Resources (MDPI) 6 (3): 40. Bibcode:2017Resou...6...40M. doi:10.3390/resources6030040.
Bau M. (1991). «Rare-earth element mobility during hydrothermal and metamorphic fluid-rock interaction and the significance of the oxidation state of europium». Chemical Geology93 (3–4): 219-230. Bibcode:1991ChGeo..93..219B. doi:10.1016/0009-2541(91)90115-8.