Why might mineral assemblages remain at a metastable state?
A material in a metastable state can reach a lower energy (more stable) state. However, there is a barrier, called the activation energy, that must be overcome first. If the material lacks sufficient energy (usually thermal energy – it’s not hot enough), the transition will be very slow, and a significant amount of material will remain in the metastable state for a very long time. This contrasts with an unstable state, where the activation barrier is either absent or very small in relation to ambient conditions. The activation barrier exists when the material must pass through some transition state less stable than either the metastable or stable state. An example of a metastable mineral is diamond, which is metastable with respect to graphite, the more stable allotrope of carbon. Look up “energy diagrams” to see a graph – it really helps. The article linked below contains a good picture.
