Goldich Stability Series

The Goldich Stability Series describes the relative order in which common rock-forming silicate minerals resist chemical weathering at Earth’s surface. The rate of weathering of silicate rocks such as granite and gneiss, for a given grain size, is related to the relative chemical stabilities of the minerals they contain, and those stabilities can be empirically ranked. ^[1] The series has a profound and immediately recognizable parallel: the stability order of minerals in the weathering environment is the same as the order in which minerals crystallize in Bowen’s Reaction Series. ^[1] That parallel is not coincidental - it arises from fundamental differences in the bonds that hold these minerals together and in the degree to which each mineral is in equilibrium with conditions at Earth’s surface.

The Mafic-Felsic Stability Series

The mafic-felsic series ranks the common sand- and silt-sized rock-forming minerals from least stable to most stable. In order of increasing stability, the mafic minerals are: olivine, Ca plagioclase, pyroxene, Ca-Na plagioclase, amphibole, Na-Ca plagioclase, Na plagioclase, biotite. The felsic minerals, continuing the series toward greater stability, are: K-feldspar, muscovite, and quartz. ^[1]

This ranking was established through empirical study of sand- and silt-sized particles in soil profiles. ^[1] The practical meaning of the ranking is direct: olivine is the first mineral to be destroyed during weathering of a rock such as basalt or peridotite, while quartz persists through weathering cycles and accumulates as a residual grain. In a mature soil or a mature sandstone, olivine and pyroxene are absent, while quartz and possibly muscovite are the dominant remaining silicate minerals.

Connection to Crystallization Temperature and Bond Type

Two linked explanations account for why high-temperature minerals are the least stable at the surface. First, minerals that crystallize at high temperatures - such as olivine - have the greatest degree of disequilibrium with surface weathering temperatures, and thus tend to be less stable than minerals that crystallize at lower temperatures such as quartz. ^[1] This is a thermodynamic argument: a mineral that forms at 1200°C is not in chemical equilibrium with a surface environment at 20°C; the system will tend to drive reactions that bring it back toward equilibrium by decomposing the mineral.

Second, and more directly, the high-temperature minerals are bonded with weaker ionic or ionic-covalent bonds, whereas quartz is bonded with strong covalent bonds. ^[1] The Si-O bond in quartz is one of the strongest bonds in common minerals, which is why quartz resists both dissolution and hydrolysis so effectively. Olivine’s bonds, by contrast, involve relatively weak electrostatic attractions between cations and the silicate framework that are easily broken by acidic water.

The Clay-Size Stability Series

For very fine-grained (clay-size) particles, the stability ranking may differ somewhat from that of sand- and silt-size particles of the same minerals. ^[1] The clay-size stability series ranks minerals on a 15-point scale, from least stable to most stable: (1) gypsum and halite; (2) calcite, dolomite, and apatite; (3) olivine, amphiboles, and pyroxenes; (4) biotite; (5) Na plagioclase, Ca plagioclase, K-feldspar, and volcanic glass; (6) quartz; (7) muscovite; (8) vermiculite; (9) smectite; (10) pedogenic (soil) chlorite; (11) allophane; (12) kaolinite and halloysite; (13) gibbsite and boehmite; (14) hematite, goethite, and magnetite; (15) anatase, titanite, rutile, ilmenite (all titanium-bearing minerals), and zircon. ^[1]

Several features of this clay-size series deserve attention. The secondary minerals - clay minerals such as kaolinite and smectite, and iron oxides such as hematite and goethite - appear at the stable end of the spectrum. This is not coincidental: these minerals formed under weathering conditions and are therefore in relative chemical equilibrium with the surface environment. By contrast, the primary silicate minerals from parent rocks (olivine, pyroxenes, feldspars) remain near the unstable end, confirming that they are fundamentally out of equilibrium at Earth’s surface. The titanium-bearing minerals and zircon are the most stable of all, which is why these heavy minerals persist as detrital grains through multiple sedimentary cycles and are used as age indicators in geochronology.

Significance

The Goldich Stability Series is the framework that connects the mineralogy of source rocks to the mineralogy of the sediments and sedimentary rocks derived from them. A sedimentologist reading a sandstone composition can use the series to infer the weathering history of the source terrane: an olivine-bearing sandstone reflects rapid erosion and minimal weathering, while a pure quartz sandstone reflects prolonged weathering or multiple recycling events that destroyed all less stable minerals. ^[1] The series also explains why certain minerals are so common in soils and weathering profiles while others vanish quickly.

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