Dissolution rates of actinolite and chlorite from a whole-rock experimental study of metabasalt dissolution from 2 ≤ pH ≤ 12 at 25 °C

- Individual mineral dissolution rates have been derived from whole-rock experiments.
- Dissolution rates of major minerals in a rock equal those of separate minerals.
- Results support the use of laboratory dissolution rates in geochemical modeling.

The dissolution rates of the minerals actinolite and chlorite were determined from metabasalt element release rates measured at 25 °C and 2 < pH < 12 in mixed flow reactors. At pH 2.0 and 3.2, chlorite rates are 3 and 5 times faster, respectively, than corresponding actinolite rates, whereas the Si release rates from metabasalt are intermediate between chlorite and actinolite rates. In contrast, at pH 7.2 and 12.0, chlorite, actinolite and the metabasalt release Si at the same rates within analytical uncertainties. At pH 6.3, it was only possible to obtain the chlorite dissolution rate; at this pH the measured chlorite dissolution rate is 10− 11.86 mol/m2/s. Mineral dissolution rates obtained in this study are within the range of corresponding values reported in the literature. This observation suggests that the dissolution rates of major-constituent minerals in a multi-phase rock are not affected by the presence of the other minerals. This conclusion validates the common assumption that the dissolution rate of an individual mineral is equal to that of the same mineral in a dissolving multi-mineralogic rock, at least for major constituents.