Single-crystal habits
Prismatic — long parallel faces, often capped by terminations. Tabular — flat, plate-like (barite, hanksite). Acicular — needle-like, slender (stibnite, natrolite). Bladed — broad and flat with sharp edges (kyanite). Equant — roughly cube- or sphere-like (garnet, pyrite). Pyramidal — tapering to a point (rutile, scheelite).
Aggregate habits
Botryoidal — clustered rounded masses (hemimorphite, smithsonite, malachite). Reniform — kidney-shaped (hematite). Mammillary — large smooth domes. Druzy — a coating of tiny crystals on a matrix. Dendritic — tree-like branching (native silver, pyrolusite manganese on limestone). Massive — no visible crystals, just solid mineral (lapis lazuli, jade). Granular — many small grains (peridot in olivine matrix).
Why habit predicts identity
Crystal habit is dictated by the same atomic arrangement that defines the crystal system, plus the growth-environment temperature and rate. A mineral grown slowly in an open vug will show large euhedral crystals; the same species formed quickly in a hot vein will be massive or fibrous. Knowing both the typical habit AND the typical exceptions for each major species is the difference between hobbyist guessing and professional ID.