PostImpact Alteration of the Manson Impact Structure
Abstract
Partitioning of Rare Earth Elements (REE) in whitlockite is complicated by the fact that two or more chargebalancing substitutions are involved and by the fact that concentrations of REE in natural whitlockites are sufficiently high such that simple partition coefficients are not expected to be constant even if mixing in the system is completely ideal. The present study combines preexisting REE partitioning data in whitlockites with new experiments in the same compositional system and at the same temperature (approximately 1030 C) to place additional constraints on the complex variations of REE partition coefficients and to test theoretical models for how REE partitioning should vary with REE concentration and other compositional variables. With this data set, and by combining crystallographic and thermochemical constraints with a SAS simultaneousequation bestfitting routine, it is possible to infer answers to the following questions: what is the speciation on the individual sites Ca(B), Mg, and Ca(IIA) (where the ideal structural formula is Ca(B)18 Mg2Ca(IIA)2P14O56); how are REE's chargebalanced in the crystal; and is mixing of REE in whitlockite ideal or nonideal. This understanding is necessary in order to extrapolate derived partition coefficients to other compositional systems and provides a broadened understanding of the crystal chemistry of whitlockite.
 Publication:

Lunar and Planetary Science Conference
 Pub Date:
 March 1993
 Bibcode:
 1993LPI....24..323C
 Keywords:

 Crystallography;
 Crystals;
 Mineralogy;
 Physical Chemistry;
 Rare Earth Elements;
 Thermochemistry;
 Coefficients;
 Extrapolation;
 Mathematical Models;
 SolidState Physics