\Al"lo*morph\, n. [Gr. ? other + ? form.] (Min.)
(a) 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) 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.