Incorporation of U, Pb and Rare Earth Elements in Calcite through Crystallisation from Amorphous Calcium Carbonate: Simple Preparation of Reference Materials for Microanalysis

Abstract

Uncertainty for elemental and isotopic measurements in calcite by LA‐ICP‐MS is largely controlled by the homogeneity of the reference materials (RMs) used for calibration and validation. In order to produce calcite RMs with homogeneous elemental and isotopic compositions, we incorporated elements including U, Pb and rare earth elements into calcite through heat‐ and pressure‐induced crystallisation from amorphous calcium carbonate that was precipitated from element‐doped reagent solution. X‐ray absorption spectra showed that U was present as U(VI) in the synthesised calcite, probably with a different local structure from that of aqueous uranyl ions. The uptake rate of U by our calcite was higher in comparison with synthetic calcite of previous studies. Variations of element mass fractions in the calcite were better than 12% 2RSD, mostly within 7%. The 207Pb/206Pb ratio in the calcite showed < 1% variations, while the 238U/206Pb ratio showed 3–24% variations depending on element mass fractions. Using the synthetic calcite as primary RMs, we could date a natural calcite RM, WC‐1, with analytical uncertainty as low as < 3%. The method presented can be useful to produce calcite with controlled and homogeneous element mass fractions and is a promising alternative to natural calcite RMs for U‐Pb geochronology.

Heat-Induced Dolomitization of Amorphous Calcium Magnesium Carbonate in a CO2-Filled Closed System

“…Matsunuma et al showed that pressure-induced crystallization of ACC is more efficient for doping incompatible elements into crystals than crystallization in supersaturated solutions. Recently, calcite incorporating large amounts of incompatible elements such as Sr 2+ , Ba 2+ , and U 6+ was synthesized by heat-induced crystallization of element-doped ACC. , The dolomitization by a solid-phase reaction from ACMC may also facilitate the synthesis of element-doped dolomite.…”

“…Recently, calcite incorporating large amounts of incompatible elements such as Sr 2+ , Ba 2+ , and U 6+ was synthesized by heatinduced crystallization of element-doped ACC. 44,45 The dolomitization by a solid-phase reaction from ACMC may also facilitate the synthesis of element-doped dolomite.…”

“…On the other hand, ACC easily crystallizes into calcite by heating in air . This crystallization process is considered to proceed by solid-state transformation. ,, The crystallization by solid-state transformation has a variety of applications, including the study of biominerals, , selective crystallization into desired polymorphs (calcite ,, or aragonite , ), the addition of large amounts of impurities to crystals, − reference materials, and synthesis of nanoporous calcite with a high specific surface area …”

“…37 This crystallization process is considered to proceed by solid-state transformation. 30,33,34 The crystallization by solidstate transformation has a variety of applications, including the study of biominerals, 38,39 selective crystallization into desired polymorphs (calcite 30,33,34 or aragonite 40,41 ), the addition of large amounts of impurities to crystals, 42−44 reference materials, 45 and synthesis of nanoporous calcite with a high specific surface area. 46 Amorphous calcium magnesium carbonate (ACMC) with dolomite composition may be a precursor for dolomite formation.…”

Atomic spectrometry update – a review of advances in environmental analysis

“…The process of ‘additive manufacturing’ clearly has great potential in the production of matrix-matched RMs. The incorporation of Pb, REEs and U into calcite involved 207 heat- and pressure-induced crystallisation from amorphous calcium carbonate that had been precipitated from an element-doped reagent solution. The doped elements in the resulting calcite RMs were homogenously distributed (<12%, 2RSD).…”