Allomorph
Allomorph ({not transcribed}) , noun
[Greek {not transcribed} other + morfh` form.]
(a)
(Mineralogy) 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.
(b)
(Mineralogy) A variety of pseudomorph which has undergone partial or complete change or substitution of material; -- thus limonite is frequently an allomorph after pyrite. — G. H. Williams