What are the conditions governs isomorphous substitution?

Isomorphous substitution occurs when one ion in a mineral's crystal structure is replaced by another ion of similar size and charge without significantly altering the mineral's overall structure. The conditions that govern this process include the ionic radius, where the substituting ion must be close in size to the original ion; the valence, requiring similar charge; and the relative abundance of the ions in the environment. Additionally, temperature and pressure can influence the extent of substitution, as higher temperatures can enhance mobility and allow for greater substitution.