A kind of pseudomorph, in which there has been a change of physical characters, by a change in crystal structure without alteration of chemical composition, as the change of aragonite to calcite; called also allomorph.

a mineral of the same chemical composition, but which crystalizes in a different crystal system as the original it replaced

Minerals which have the same composition but different crystal structures.

A taxonomic variant observed within a species, for which a more specific term has not been assigned.