Crystal habit 219561 220817075 2008-06-21T18:57:54Z 88.105.66.250 /* 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)]]