Interstitial Substitution

Substitution in which interstitial ions are added or removed. This is most common in cyclosilicate minerals, which have channel-like structures (e.g., beryl or zeolites) or in clay minerals, which can accommodate ions between their silicate sheets. The charge of interstitial ions is often balanced by substitutions in the crystal lattice. For example, for interstitial ions in the channels of beryl (R):

Some or all content above used with permission from J. H. Wittke.