Crystal habit is the overall shape a mineral tends to take as it grows. It describes what a crystal or a mass of crystals looks like in the hand: long and pencil-like, flat like a book, rounded like a bunch of grapes, or branching like a fern. Habit depends on a mineral's internal structure and on the conditions where it grew, and it is one of the first clues a gemologist or rockhound uses to identify rough material.
Habit, form and crystal system
Three ideas overlap here and are easy to mix up. The crystal system is the symmetry of the atomic lattice, such as cubic or trigonal. A crystal form is a set of identical faces related by that symmetry, such as the eight faces of an octahedron. Habit is the shape you actually see, which may combine several forms and reflect how fast the crystal grew in each direction.
A mineral can have more than one habit. Corundum can grow as six-sided barrels or flat plates. Quartz can form long prisms, stubby points, microscopic crystal crusts or solid microcrystalline masses. Growth temperature, the space available, the chemistry of the surrounding fluid and impurities all affect which habit appears.
Common habit terms
| Habit | What it looks like | Gem examples |
|---|---|---|
| Prismatic | Elongated, with parallel faces running along the length | Beryl, tourmaline, quartz, topaz |
| Columnar | Thick prisms or column-like bundles | Some tourmaline, beryl |
| Tabular | Flat, plate-like, wider than thick | Ruby from some deposits, wulfenite, barite |
| Bladed | Long and flat, like a knife blade | Kyanite |
| Acicular | Thin and needle-like | Rutile, some tourmaline needles |
| Fibrous | Very fine parallel fibers | Crocidolite, the precursor of tiger's eye |
| Equant | About as wide in all directions | Garnet, spinel, diamond |
| Octahedral | Eight triangular faces, like two pyramids base to base | Diamond, spinel, magnetite |
| Dodecahedral | Twelve faces, usually rhomb-shaped | Garnet |
| Cubic | Six square faces | Pyrite, fluorite |
| Botryoidal | Rounded, grape-like clusters | Malachite, prehnite, chalcedony, hematite |
| Reniform | Kidney-shaped rounded masses | Hematite |
| Dendritic | Branching, tree- or fern-like patterns | Manganese oxides in dendritic agate, native copper |
| Druzy | A crust of many tiny crystals lining a surface | Quartz, uvarovite garnet |
| Massive | No visible crystal shape, a solid mass | Turquoise, lapis lazuli, rose quartz, jade |
| Grainy (saccharoidal) | A mass of small, roughly equal grains, like sugar | Some garnet rock, marble |
Prismatic and columnar
Prismatic crystals are longer than they are wide, with faces running parallel to the long direction. Many favorite gem crystals grow this way. Aquamarine and other beryls form six-sided prisms, sometimes very large and clean. Tourmaline forms prisms with lengthwise grooves (striations) and a rounded triangular cross section. Topaz forms prisms with lengthwise striations and a cleavage across them.
Tabular and bladed
Tabular crystals are flat. Ruby from marble deposits often grows as flat hexagonal plates, while many sapphires grow as tapered barrels. Kyanite grows as long, flat blades, and its hardness differs along and across the blade.
Acicular and fibrous
Acicular means needle-like. Fine rutile needles inside quartz create the golden "hair" of rutilated quartz, and oriented rutile needles inside corundum produce the silk that makes star sapphires possible. Fibrous habit, with fibers packed side by side, gives chatoyancy. Tiger's eye forms when quartz replaces fibrous crocidolite, keeping the fibrous pattern that creates its moving band of light.
Equant and octahedral
Equant crystals are about the same size in every direction. Garnet is the classic case, growing as rounded dodecahedra or trapezohedra that can look almost like balls. Diamond and spinel often grow as octahedra, and rough diamonds in this shape are prized for rough diamond jewelry.
Botryoidal and reniform
Botryoidal comes from the Greek for a bunch of grapes. These rounded masses build up in layers from mineral-rich solutions, often in open cavities. Malachite and prehnite commonly grow this way, and cutting through a botryoidal mass of malachite reveals its concentric bands. Reniform masses are similar but larger and kidney-shaped.
Dendritic
Dendritic growth branches like a tree. Dendrites of manganese or iron oxide inside agate look like tiny plants and give dendritic agate its name. They are mineral growths, not fossils.
Druzy
A druzy (also spelled drusy) surface is coated with many small crystals that sparkle. Druzy quartz lines the insides of geodes, and uvarovite forms bright green druzy crusts of tiny garnet crystals. The druzy page covers how these crusts are set in jewelry.
Massive and grainy
Massive material shows no outer crystal shape at all. Turquoise, lapis lazuli and rose quartz usually occur this way. The material may still be crystalline at a microscopic scale, as jade and chalcedony are, but you cannot see individual crystals.
Why habit varies
A crystal grows by adding atoms to its faces. Faces that grow slowly end up large, and faces that grow fast shrink and may vanish. Changes in temperature, pressure, fluid chemistry and impurity levels shift those growth rates, so the same mineral can look very different from one deposit to another.
Space matters too. Crystals that grow into an open pocket, as in a granite pegmatite, can develop full faces on every side. Crystals growing in solid rock compete for room and often end up as rounded grains. Corrosion after growth can round edges, which is why many diamonds have curved faces. River transport wears crystals down further, so alluvial rough is often waterworn pebbles with little habit left.
Using habit to identify rough
Habit is a strong field clue when combined with other observations. A six-sided prism with flat ends suggests beryl. A prism with deep striations and a triangular outline points to tourmaline. A rounded twelve-sided crystal in mica schist is very likely garnet. Diamond octahedra often show small triangular pits on their faces called trigons, which are a classic sign of natural diamond rough.
Gem buyers in mining areas learn these shapes, along with striation patterns, luster and weight in the hand. Habit alone is not proof. Glass can be molded into crystal shapes, waterworn rough loses its faces, and several minerals share similar habits. Confirmation still comes from tests such as refractive index and specific gravity, covered on the gemological instruments page.
Habit and the finished gem
Habit shapes how a crystal is cut. Long tourmaline and beryl prisms yield long gems, which is one reason emerald cuts and elongated shapes are common for these stones. Flat ruby crystals limit depth, so cutters often produce shallower stones from them. Diamond octahedra can be sawn in half to make two round brilliants with little waste, a fact that helped shape the proportions of the modern brilliant.
Frequently asked questions
What is the difference between crystal habit and crystal form?
A crystal form is a set of matching faces defined by symmetry, such as a cube or octahedron. Habit is the overall shape the crystal actually grows into, which can combine several forms.
What does botryoidal mean?
It describes rounded, grape-like masses built up in layers. Malachite, prehnite and some chalcedony and hematite grow this way.
Can one mineral have several habits?
Yes. Quartz, corundum, calcite and fluorite all grow in different habits depending on the conditions where they formed.
Is massive turquoise made of crystals?
Yes, at a microscopic scale. Turquoise crystals large enough to see are rare, so the material usually forms solid masses, veins and nodules.