What is epitaxy in mineralogy ?

Epitaxy : definition

Epitaxy is a phenomenon of oriented growth, one relative to the other, of two crystals belonging to two different mineral species. To be carried out, epitaxy requires the existence of a certain number of common symmetry elements in the crystal lattices of the minerals concerned. Among the classic epitaxies we note rutile crystals on titaniferous hematites (ilmenites) or quartz crystals on orthoclase (photo on the right).