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Schools in Science


As fluids travel through the crust, chemical disequilibrium drives reactions between the fluid and the minerals in the surrounding rocks. At a fundamental level, many of these fluid–rock interactions are solubility-driven mineral replacement reactions.

By mimicking natural textures in the lab we can understand some of the processes and conditions that drive these reactions.

Comparison of the microtextures of porous gold from the Aginskoe deposit (ac) with those of synthetic Au (and Au-Ag alloy) obtained experimentally via the de-alloying of calaverite at 200 °C and pH24.6°C = 1.86 (df). Horizontal stripes in e are due to charging on the uncoated, freshly cut surface.

Reference:Microporous gold: Comparison of textures from Nature and experiments. VM Okrugin et al. 2014, American Mineralogist 99 (5-6), 1171-1174

Textures obtained from experimental dolomitization of calcite grains in closed system experiments (200 °C, vapor-saturated pressure). For a, b, starting material is a ground marble and running time 4 days; for c–e, single Iceland spar crystal with a running time of 11 days. a–c Dolomite forms rims around the calcite grains. Coarse porosity occurs at the reaction interface (c), and a large cavity commonly developed between the calcite and the dolomite for runs that used the marble sample (a). d Detail of the grain in (c), showing that finer porosity also forms within the dolomite. e Dolomite forms idiomorphic crystals on the outside of the grains

Reference:Grain boundaries as microreactors during reactive fluid flow: experimental dolomitization of a calcite marble. B Etschmann et al. 2014, Contributions to Mineralogy and Petrology 168 (2), 1-12