Allomorph

Webster's Dictionary of the English Language

·noun A variety of pseudomorph which has undergone partial or complete change or substitution of material;

— thus limonite is frequently an allomorph after pyrite.

II. Allomorph ·noun Any one of two or more distinct crystalline forms of the same substance; or the substance having such forms;

— as, carbonate of lime occurs in the allomorphs calcite and aragonite.