Geochemistry

Magma Writ Small

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Science  11 Oct 2013:
Vol. 342, Issue 6155, pp. 163
DOI: 10.1126/science.342.6155.163-b

Solid phases that precipitate from supersaturated solutions often form from the aggregation or self-organization of molecular clusters or nanoparticles. These undersaturated precursors have been documented in a number of materials for crystals growing from aqueous solution; however, at more extreme conditions, such as in magmatic systems composed of hot melts, evidence has been more circumstantial. Through a series of high-temperature quenching experiments from 950° to 1180°C, Helmy et al. demonstrate that Pt- and As-rich nanoscale phases form in sulfidic melts despite being present in low concentrations and far from saturation for macroscopic crystalline minerals. If Pt and other noble metals preferentially form continuums of nanoscale associations with As and related elements instead of homogeneously dissolving in the melt phase, their partitioning will largely depend on surface thermodynamics instead of chemical properties determined by simple partition coefficient experiments.

Nat. Commun. 4, 2405 (2013).

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