thumb|upright=1.35|[[Smoky quartz with spessartine on top of feldspar matrix, featuring different crystal habits (shapes)]]
In mineralogy, crystal habit is the characteristic external shape of an individual crystal or aggregate of crystals. The habit of a crystal is dependent on its crystallographic form and growth conditions, which generally creates irregularities due to limited space in the crystallizing medium (commonly in rocks).
Crystal forms
Recognizing the habit can aid in mineral identification and description, as the crystal habit is an external representation of the internal ordered atomic arrangement.
Aggregate habits
{| class="wikitable"
!Habit
!Image
!Description
!Common example(s)
|-
|Acicular
|
|Needle-like, slender, and end-tapered prisms growing in a radial/globular fashion.
|natrolite, scolecite, yuanfuliite
|-
|Arborescent
|
|Tree-like crystals growing similar to branches.
|Native copper, gold, native silver
|-
|Capillary/Filiform
|
|Hair-like or thread-like, extremely fine
| byssolite, millerite
|-
|Colloform/Nodular/Tuberose
|
|Rounded, finely banded deposits with irregular concentric protuberances
| agate, baryte, sphalerite
|-
|Concentric
|
|Circular ring aggregates around a center. This habit is found in cross-sections from reniform/mamillary habits, and also from elongated stalactites of amethyst (quartz), malachites, rhodocrosite, and others
|agate, quartz, malachite, rhodocrosite
|-
|Dendritic
|
|Root-like, branching in one or more direction from central point
| Native copper, gold, romanechite, magnesite, native silver
|-
|Druse/Encrustation
|
|Aggregate of crystals coating a surface or cavity, usually found in geodes and some fossils
|azurite, celestine, calcite, uvarovite, malachite, quartz
|-
|Fibrous/Asbestiform
|
|Extremely slender prisms forming muscle-like fibers
|actinolite, asbestos, baryte, kyanite, gypsum, nitratine, stilbite, serpentine group
|-
|Foliated/Micaceous/Lamellar
|
|Layered crystal planes, parting into thin sheets
|biotite, hematite, muscovite, lepidolite, molybdenite
|-
|Granular
|
|Aggregates of diminute anhedral crystals in matrix or other surface
|andradite, bornite, scheelite, quartz, uvarovite
|-
|Hopper
|
|Outer portions of cubes grow faster than inner portions, creating a concavity similar to that of a hopper
|bismuth (artificial), halite, galena
|-
|Oolithic
|
|Small spheres or grains (commonly flattened) that resemble eggs
|aragonite, calcite
|-
|Pisolitic
|
|Rounded concentric nodules often found in sedimentary rocks. Much larger than oolithic
| aragonite, bauxite, calcite, pisolite
|-
|Platy/Tabular/Blocky
|
|Flat, tablet-shaped, prominent pinnacoid
|baryte, feldspar, topaz, vanadinite, wulfenite
|-
|Plumose
|
|Fine, feather-like scales
|aurichalcite, okenite, mottramite
|-
|Radial/Radiating/Divergent
|
|Radiating outward from a central point without producing a star (crystals are generally separated and have different lengths).
|aenigmatite, atacamite, epidote, pyrophyllite, stibnite
|-
|Reticulated
|
|Crystals forming triangular net-like intergrowths.
|cerussite, rutile
|-
|Rosette/Lenticular
|
|Platy, radiating rose-like aggregate (also lens shaped crystals)
|gypsum, baryte, calcite
|-
|Stalactitic
|
|Forming as stalactites or stalagmites; cylindrical or cone-shaped. Their cross-sections often reveal a "concentric" pattern
|calcite, chalcedony, chrysocolla, goethite, malachite, romanechite
|-
|Stellate
|
|Star-like, radial fibers found inside spherical habits, such as mamillary or reniform.
| hematite, pectolite, shattuckite, wavellite
|-
|}
Asymmetrical/Irregular habits
{| class="wikitable"
!Habit
!Image
!Description
!Common example(s)
|-
|Amygdaloidal
|
|Like embedded almonds
|heulandite, stilbite, zircon
|-
|Hemimorphic
|
|Doubly terminated crystal with two differently shaped ends
|elbaite, hemimorphite, olivine
|-
|Massive/Compact
|
|Shapeless, no distinctive external crystal shape
|limonite, turquoise, cinnabar, quartz, realgar, lazurite
|-
|Sceptered
|
|Crystal growth stops and continues at the top of the crystal, but not at the bottom. Exceptional aggregates of this habit (such as quartz) are often referred as "Elestial".
|baryte, calcite, marcasite, quartz
|-
|}
Symmetrical habits
{| class="wikitable"
!Habit
!Image
!Description
!Common example(s)
|-
|Cubic
|
|Cube-shaped
|fluorite, pyrite, galena, halite
|-
|Dodecahedral
|
|Dodecahedron-shaped, 12-sided. Central facet can vary.
|garnet, pyrite
|-
|Enantiomorphic
|
|Mirror-image habit (i.e. crystal twinning) and optical characteristics; right- and left-handed crystals
|aragonite, gypsum, quartz, plagioclase, staurolite
|-
|Hexagonal
|
|Hexagonal prism (six-sided)
|beryl, galena, quartz, hanksite, vanadinite
|-
|Icositetrahedral
|
|Icositetrahedron-shaped, 24-faced
|analcime, spessartine
|-
|Octahedral
|
|Octahedron-shaped, square bipyramid (eight-sided)
|diamond, fluorine, fluorite, magnetite, pyrite
|-
|Prismatic
|
|Elongate, prism-like: may or not present well-developed crystal faces parallel to the vertical axis
|beryl, tourmaline, vanadinite
|-
|Rhombohedral
|
|Rhombohedron-shaped (six-faced rhombi)
|calcite, magnesite, rhodochrosite, siderite
|-
|Scalenohedral
|
|Scalenohedron-shaped, pointy ends
|calcite, rhodochrosite, titanite
|-
|Tetrahedral
|
|Tetrahedron-shaped, triangular pyramid (four-sided)
|chalcopyrite, tetrahedrite, sphalerite, magnetite
|-
|}
Rounded/Spherical habits
{| class="wikitable"
!Habit
!Image
!Description
!Common example(s)
|-
|Botryoidal
|
|Grape-like, large and small hemispherical masses, nearly differentiated/separated from each other
|calcite, chalcedony, halite, plumbogummite, smithsonite
|-
|Globular
|
|Isolated hemispheres or spheres
|calcite, fluorite, gyrolite
|-
|Mammillary
|
|Breast-like: surface formed by intersecting partial spherical shapes, larger version of botryoidal and/or reniform, also concentric layered aggregates.
|chalcedony, hematite, malachite
|-
|Reniform
|
|Irregular kidney-shaped spherical masses
|cassiterite, chalcedony, chrysocolla, hematite, hemimorphite fluorite, goethite, greenockite, malachite, rhodochrosite, smithsonite, mottramite, wavellite
|-
|}
See also
- Abnormal grain growth
- Grain growth
- Crystal structure