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 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 sapphires 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 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.
|Acicular||Needle-like, slender and/or tapered||Rutile in quartz|
|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|
|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||Geodes|
|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|
|Stalactitic||Forming as stalactites or stalagmites; cylindrical or cone-shaped||Rhodochrosite|
|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||Zeolites|
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