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Crystal habit

In , crystal habit is the characteristic external shape of an individual or crystal group. A single crystal's habit is a description of its general shape and its crystallographic forms, plus how well developed each form is.

Recognizing the habit may help in identifying a . When the faces are well-developed due to uncrowded growth a crystal is called , one with partially developed faces is subhedral, and one with undeveloped crystal faces is called anhedral. The long axis of a euhedral quartz crystal typically has a six-sided prismatic habit with parallel opposite faces. Aggregates can be formed of individual crystals with euhedral to anhedral grains. The arrangement of crystals within the aggregate can be characteristic of certain minerals. For example, minerals used for insulation often grow in a fibrous habit, a mass of very fine fibers.Klein, Cornelis, 2007, Minerals and Rocks: Exercises in Crystal and Mineral Chemistry, Crystallography, X-ray Powder Diffraction, Mineral and Rock Identification, and Ore Mineralogy, Wiley, third edition, Wenk, Hans-Rudolph and Andrei Bulakh, 2004, Minerals: Their Constitution and Origin, Cambridge, first edition,

The terms used by mineralogists to report crystal habits describe the typical appearance of an ideal mineral. Recognizing the habit can aid in identification as some habits are characteristic. Most minerals, however, do not display ideal habits due to conditions during . Euhedral crystals formed in uncrowded conditions with no adjacent crystal grains are not common; more often faces are poorly formed or unformed against adjacent grains and the mineral's habit may not be easily recognized. Factors influencing habit include: a combination of two or more crystal forms; trace impurities present during growth; and growth conditions (i.e., heat, pressure, space); and specific growth tendencies such as growth striations. 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 form elongate barrel-shaped crystals, those found in form stout tabular crystals. Ordinarily, the latter habit is seen only in . Sapphire and ruby are both varieties of the same mineral: .

Some minerals may replace other existing minerals while preserving the original's habit: this process is called . A classic example is tiger's eye , replaced by . While quartz typically forms prismatic (elongate, prism-like) crystals, in tiger's eye the original fibrous habit of crocidolite is preserved.

The names of crystal habits are derived from:

  • Predominant crystal faces (prism – prismatic, pyramid – pyramidal and pinacoid – platy)
  • Crystal forms (cubic, octahedral, dodecahedral)
  • Aggregation of crystals or aggregates (fibrous, botryoidal, radiating, massive)
  • Crystal appearance (foliated/lamellar (layered), dendritic, bladed, acicular, lenticular, tabular (tablet shaped))

List of crystal habits
Acicular Needle-like, slender and/or tapered,

Like embedded almonds, subhedral
Bladed Blade-like, slender and flattened,
or globular Grape-like, hemispherical masses, , , , , ,
Columnar Similar to fibrous: Long, slender prisms often with parallel growth, /Selenite
Coxcomb Aggregated flaky or tabular crystals closely spaced.,
Cubic shape, ,
Dendritic or arborescent Tree-like, branching in one or more direction from central point and other -oxide minerals, , native
Dodecahedral Rhombic dodecahedron, 12-sided
Drusy or encrustation Aggregate of minute crystals coating a surface or cavity, , ,
Enantiomorphic Mirror-image habit (i.e. ) and optical characteristics; right- and left-handed crystalsQuartz, ,
Equant, stout Length, width, and breadth roughly equal,
Fibrous Extremely slender prisms, (i.e. )
Filiform or capillary Hair-like or thread-like, extremely finemany
Foliated or micaceous or lamellar (layered) Layered structure, parting into thin sheets (, , etc.)
Granular Aggregates of anhedral crystals in matrix,
Hemimorphic Doubly terminated crystal with two differently shaped ends,
Hexagonal shape, six-sided,
Like cubic, but outer portions of cubes grow faster than inner portions, creating a concavity, , synthetic
Mammillary Breast-like: surface formed by intersecting partial spherical shapes, larger version of botryoidal, also concentric layered aggregates,
Massive or compact Shapeless, no distinctive external crystal shape, , ,
Nodular or tuberose Deposit of roughly spherical form with irregular protuberances, various
Octahedral , eight-sided (two pyramids base to base),
Platy Flat, tablet-shaped, prominent pinnacoid
Plumose Fine, feather-like scales, ,
Prismatic Elongate, prism-like: well-developed crystal faces parallel to the vertical axis,
Pseudo-hexagonal Hexagonal appearance due to cyclic twinning,
Radiating or divergent Radiating outward from a central point, suns
Reniform or colloform Similar to botryoidal/mamillary: intersecting kidney-shaped masses, ,
Reticulated Crystals forming net-like intergrowths
Rosette or lenticular (lens shaped crystals) Platy, radiating rose-like aggregate, (i.e. Desert rose)
Sphenoid Wedge-shaped
Stalactitic Forming as stalactites or stalagmites; cylindrical or cone-shaped, , Malachite
Stellate Star-like, radiating,
Striated Not a habit per se, but a condition of lines that can grow on certain crystal faces on certain minerals, , , ,
Tabular (also stubby or blocky) More elongated than equant, slightly longer than wide, flat tablet-shaped,
Tetrahedral -shaped crystals, ,
Wheat sheaf Aggregates resembling hand-reaped wheat sheaves

See also

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