In general, minerals are most stable at the temperature and pressure at which they form. In the case of the igneous rock minerals described in Bowen's Reaction Series, the higher temperature minerals (such as olivine, pyroxene, etc.), when exposed at the surface, will be farthest from their comfort zone, and will therefore chemically weather at a faster rate. Quartz, at the other end of Bowen's, is closer to its preferred temperature and should therefore be more stable (and it is). This is one reason why we find quartz sand at the beach, instead of olivine sand.

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