Goldich dissolution series

Olivine weathering to iddingsite within a mantle xenolith, a common reaction within the series

The Goldich dissolution series is a way of predicting the relative stability or weathering rate of various minerals on the Earth's surface. S. S. Goldich came up with the series in 1938^[1] after studying soil profiles. He found that minerals that form at higher temperatures and pressures are less stable on the surface than minerals that form at lower temperatures and pressures.^[2] This pattern follows the same pattern of the Bowen's reaction series, with the minerals that are first to crystallize also the first the undergo chemical weathering.

In 1938, Samuel Goldich published a study of the weathering of various igneous rocks in which he concluded that igneous silicate minerals weather in an order much like that of Bowens Reactions Series, with mafic silicates the most susceptible to weathering and quartz the least susceptible. The diagram below shows a modified form of Goldich's series, which has subsequently been confirmed experimentally. Zircon and several non-silicates have been added below in the apparent order of their susceptibility of weathering (the position of calcite relative to olivine and anorthite is debatable). The diagram below shows that the order of this weathering series agrees well with the least bond strength in each of the minerals involved. That seems reasonable, because weathering, or the destruction of minerals, requires breaking of bonds in those minerals. The only special provision is to bear in mind that some minerals consist sufficiently of strongly bonded cations that a weakly bonded cation can be leached from the surface of a mineral grain without destruction of the entire mineral grain. That has been demonstrated experimentally to be the case with alkali feldspars, where weathering can preferentially remove the alkali cation (K1+ or Na1+) but leave an Al-Si remnant structure on the surface of feldspar grains3. The diagram also has application for non-igneous materials. For example, aragonite and calcite are both present in marine sediments, but aragonite rarely survives in ancient limestones, where calcite is abundant. The weaker bond formed by Ca2+ in nine-fold coordination in aragonite, rather than the stronger bond of Ca2+ in six-fold coordination in calcite, explains aragonite's greater susceptibility to dissolution. Halite, an even more soluble sedimentary mineral, has even weaker bonds, and niter, a mineral that hardly survives in nature at all, has the weakest bonds.^[3]

References

1. ↑ Goldich, S. S. (1938). "A Study in Rock Weathering". Journal of Geology. 46: 17–58. Bibcode:1938JG.....46...17G. doi:10.1086/624619. 
2. ↑ Prothero & Schwab, Donald R. & Fred (1996). Sedimentary Geology. W. H. Freeman. p. 24. ISBN 0-7167-2726-9. 
3. ↑ Goldich, S.S., 1938, A study in rock-weathering: Journal of Geology 46: 17-58. 2 See Table 7.1 of Langmuir, D., 1997, Aqueous Environmental Geochemistry: Prentice Hall, 600 p. 3 Chou, L., & Wollast, R., 1984, Study of the weathering of albite at room temperature and pressure with a fluidized bed reactor: Geochimica et Cosmochimica Acta 48: 2205-2217