DESCRIPTIVE CRYSTAL HABITS

The following terms are more descriptive than the technical terms and are therefore easier to understand. These are some of the more common descriptive terms used to portray certain crystal habits of both individual and aggregate crystal varieties.

Individual crystal varieties:

Acicular
Bladed
Blocky
Equant
Fibrous
Platy
Prismatic
Stubby
Tabular

Aggregate Crystal Varieties:

Botryoidal
Dendritic
Druse
Geode
Granular
Globular
Lamellar
Mammillary
Micaceous
Nodular
Oolitic
Pisolitic
Radiating
Rosetta
Stalactitic

Vugs

Individual crystal varieties:

Acicular: Long and needle-like, thinner than prismatic but thicker than fibrous. Natrolite forms crystals that are a good example of acicular crystals.
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Bladed: Elongated and flattened like a blade of grass. More elongated than tabular and thicker than platy. Barite forms crystals that are a good example of bladed crystals.
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Blocky: Rectangular and box-like, but not necessarily with flat sides. More elongated than equant but less elongated than prismatic. Orthoclase forms crystals that are a good example of blocky crystals.
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Equant: Any three perpendicular axis through the crystal are more or less equal. Can be used to describe rounded as well as angular crystals. Fluorite forms crystals that are a good example of equant crystals.
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Fibrous: Thinner than acicular crystals in either individual crystals or in a tight compact mass. Serpentine forms crystals that are a good example of fibrous crystals.
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Platy: Flattened and thin crystals (like plates) but wider than bladed and thinner than tabular. Albite crystals are a good example of platy crystals.
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Prismatic: Elongated crystals that are thicker than needles (acicular). Apatite forms a good example of prismatic crystals.
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Stubby: Slightly more elongated than equant but not as elongated as prismaticand possibly more rounded than blocky. Cassiterite forms crystals that are a good example of stubby crystals.
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Tabular: Book-like (tablets) that are thicker than platy and not as elongated as bladed. Torbernite forms crystals that are a good example of tabular crystals.
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Aggregate Crystal Varieties:

Botryoidal: Resembling grape bunches with interlocking rounded masses. Formed from acicular or bladed crystals growing from a common site for each rounded mass. The tops of the crystals are smooth and blend so that individual crystal edges are indiscernable except from broken edges. Smithsonite forms aggregates that are a good example of this form.
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Dendritic: A growth of crystals on a surface or as an inclusion that forms plant-like patterns similar to "Jack Frost" on windows. Pyrolusite forms aggregates that are a good example of this form.
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Druse: Outwardly oriented crystals usually lining the inside of a geode, but is also applied to other outwardly oriented crystal coatings. Amethyst, a variety of quartz, forms aggregates that are a good example of this form.
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Geode: A hollow stone embedded in a layer of rock minerallogically different from the mineral composing the outer shell of the geode (see vugs). Celestite is found in good examples of this form.
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Globular: Bubbly, rounded masses, similar to botryoidal or mammillary but less coherent. Aragonite forms aggregates that are a good example of this form.
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Granular: Crystals of a small size, less than 1 cm across, that exhibit no really discernable crystal form. Usually applied to many tiny crystals separated and dessiminated throughout a host rock. Hornblende forms crystals that are a good example of this habit.
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Lamellar: Layered masses like sheets of paper. Murmanite forms aggregates that are a good example of this form.
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Mammillary: rounded "breast-like" masses, similar to botryoidal and globular but more rounded, larger individual masses. Goethite forms aggregates that are a good example of the this form.
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Micaceous: Flaky, platy crystals compacted together in masses. Similar to lamellar but with smaller crystals. Lepidolite, a mica, forms aggregates that are a good example of this form.
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Nodular: A stone of concentric growth around a center usually composed of mostly one mineral. If broken, may show concentric rings. Forms rounded spherical to oddly shaped concretions. Pyrite forms good examples of the this form.
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Oolitic: Rounded pebble to sand sized nodules in a compact mass formed in sedimentary environs. Hematite forms masses that are a good example of the this form.
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Pisolitic: Rounded marble to pebble sized nodules in a compact mass formed in certain sedimentary enviroments. Nodules are larger than oolitic forms. Gibbsite forms masses that are a good example of the this form.
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Radiating: Distinct crystals arranged in an orientation outward from a common point. Atacamite forms aggregates that are a good example of this form.
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Rosetta: Petal-like crystals arranged in a flattened radial habit around a central point. Autunite forms aggregates that are a good example of the rosetta form.
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Stalactitic: A concretionary growth around a usually hollow tube, producing long, slowly, tappering, and rounded masses. Usually formed in caves or other voids in rocks from the precipitation of a mineral from an evaporating fluid. Rhodochrosite forms aggregates that are a good example of the form.
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Vugs: A void in a rock whose "shell" contains the same mineral as the host rock (see geode). The cavity is sometimes filled with different minerals than the host rock, however. Tourmaline is a good example of a mineral that forms inside of vugs. ^