Crystal habit
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/* List of crystal habits */
{{otheruses4|the descriptive term used in [[mineralogy]]|the [[drug addiction|addictive drug]]|methamphetamine{{!}}crystal methamphetamine}}
In [[mineralogy]], shape and size give rise to descriptive terms applied to the typical appearance, or '''habit''' of [[crystal]]s.
[[image:pyrite sun.jpg|right|thumb|300px|Pyrite sun (or dollar) in laminated shale matrix. Between tightly spaced layers of shale, the aggregate was forced to grow in a laterally compressed, radiating manner. Under normal conditions, pyrite would form cubes or pyritohedrons.]]
The many terms used by mineralogists to describe crystal habits are useful in communicating what specimens of a particular mineral often look like. Recognizing numerous habits helps a mineralogist to identify a large number of minerals. Some habits are distinctive of certain minerals, although most minerals exhibit many differing habits (the development of a particular habit is determined by the details of the conditions during the mineral formation/crystal growth). Crystal habit may mislead the inexperienced as a mineral's internal [[crystal structure|crystal system]] can be hidden or disguised.
Factors influencing a crystal's habit include: a combination of two or more crystal forms; trace impurities present during growth; [[crystal twinning]] and growth conditions (i.e., heat, pressure, space). Minerals belonging to the same crystal system do not necessarily exhibit the same habit. Some habits of a mineral are unique to its variety and locality: For example, while most [[sapphire]]s form elongate barrel-shaped crystals, those found in [[Montana]] form stout ''tabular'' crystals. Ordinarily, the latter habit is seen only in [[ruby]]. Sapphire and ruby are both varieties of the same mineral; [[corundum]].
Some minerals may replace other existing minerals while preserving the original's habit: this process is called [[Pseudomorph|pseudomorphous replacement]]. A classic example is [[tiger's eye]] [[quartz]], [[crocidolite]] [[asbestos]] replaced by [[silica]]. While quartz typically forms ''euhedral'' (well-formed), ''prismatic'' (elongate, prism-like) crystals, in tiger's eye the original ''fibrous'' habit of crocidolite is preserved.
==List of crystal habits==
{| border="1" cellpadding="2"
|'''Habit:'''
|'''Description:'''
|'''Example:'''
|-
|Acicular
|Needle-like, slender and/or tapered
|[[Rutile]] in quartz
|-
|Amygdaloidal
|Almond-shaped
|[[Heulandite]]
|-
|Anhedral
|Poorly formed, external crystal faces not developed
|[[Olivine]]
|-
|Bladed
|Blade-like, slender and flattened
|[[Kyanite]]
|-
|[[Botryoidal]] or globular
|Grape-like, hemispherical masses
|[[Smithsonite]],[[Hemimorphite]],[[Adamite]] and [[Variscite]].
|-
|Columnar
|Similar to fibrous: Long, slender prisms often with parallel growth
|[[Calcite]]
|-
|Coxcomb
|Aggregated flaky or tabular crystals closely spaced.
|[[Barite]]
|-
|Dendritic or arborescent
|Tree-like, branching in one or more direction from central point
|[[Magnesite]] in [[opal]]
|-
|Dodecahedral
|Dodecahedron, 12-sided
|[[Garnet]]
|-
|Drusy or encrustation
|Aggregate of minute crystals coating a surface
|[[Uvarovite]]
|-
|Enantiomorphic
|Mirror-image habit and optical characteristics; right- and left-handed crystals
|[[Quartz]]
|-
|Equant, stout, stubby or blocky
|Length, width, and breadth roughly equal
|[[Zircon]]
|-
|Euhedral
|Well-formed, external crystal faces developed
|[[Spinel]]
|-
|Fibrous or columnar
|Extremely slender prisms
|[[Tremolite]]
|-
|Filiform or capillary
|Hair-like or thread-like, extremely fine
|[[Natrolite]]
|-
|Foliated or micaceous
|Layered structure, parting into thin sheets
|[[Mica]]
|-
|Granular
|Aggregates of anhedral crystals in matrix
|[[Scheelite]]
|-
|Hemimorphic
|Doubly terminated crystal with two differently shaped ends.
|[[Hemimorphite]]
|-
|Mamillary
|Breast-like: surface formed by intersecting partial spherical shapes
|[[Malachite]]
|-
|Massive or compact
|Shapeless, no distinctive external crystal shape
|[[Serpentine]]
|-
|Nodular or tuberose
|Deposit of roughly spherical form with irregular protuberances
|[[Geode]]s
|-
|Octahedral
|Octahedron, eight-sided (two pyramids base to base)
|[[Diamond]]
|-
|Plumose
|Fine, feather-like scales
|[[Mottramite]]
|-
|Prismatic
|Elongate, prism-like: crystal faces parallel to [[c-axis]] well-developed
|[[Tourmaline]]
|-
|Pseudo-hexagonal
|hexagonal appearance due to cyclic twinning
|[[Aragonite]]
|-
|Pseudomorphous
|Occurring in the shape of another mineral through pseudomorphous replacement
|[[Tiger's eye]]
|-
|Radiating or divergent
|Radiating outward from a central point
|[[Pyrite]] suns
|-
|Reniform or colloform
|Similar to mamillary: intersecting kidney-shaped masses
|[[Hematite]]
|-
|Reticulated
|Acicular crystals forming net-like intergrowths
|[[Cerussite]]
|-
|Rosette
|Platy, radiating rose-like aggregate
|[[Gypsum]]
|-
|Sphenoid
|Wedge-shaped
|[[Sphene]]
|-
|Stalactitic
|Forming as stalactites or stalagmites; cylindrical or cone-shaped
|[[Rhodochrosite]]
|-
|Stellate
|Star-like, radiating
|[[Pyrophyllite]]
|-
|Striated/striations
|Surface growth lines parallel or perpendicular to a crystallographic axis
|[[Chrysoberyl]]
|-
|Subhedral
|External crystal faces only partially developed
|
|-
|Tabular or lamellar
|Flat, tablet-shaped, prominent pinnacoid
|[[Ruby]]
|-
|Wheat sheaf
|Aggregates resembling hand-reaped wheat sheaves
|[[Zeolite]]s
|}
{{Template: Mineral identification}}
[[Category:Crystallography]]
[[Category:Mineralogy]]
[[bs:Kristalni habitus]]
[[de:Kristallhabitus]]
[[es:Hábito cristalino]]
[[fr:Habitus (minéralogie)]]
[[he:צורות של גבישים]]
[[lv:Habituss]]
[[no:Krystallform]]
[[nds:Kristallindruck]]
[[pl:Pokrój kryształu]]
[[pt:Hábito cristalino]]
[[ro:Habitus]]
[[ru:Габитус кристаллов]]
[[sk:Habitus kryštálu]]
[[fi:Asu (mineralogia)]]