Crystal habit

Recognizing the habit can aid in mineral identification and description, as the crystal habit is an external representation of the internal ordered atomic arrangement.^[1] Most natural crystals, however, do not display ideal habits and are commonly malformed. Hence, it is also important to describe the quality of the shape of a mineral specimen:

• Euhedral: a crystal that is completely bounded by its characteristic faces, well-formed. Synonymous terms: idiomorphic, automorphic;
• Subhedral: a crystal partially bounded by its characteristic faces and partially by irregular surfaces. Synonymous terms: hypidiomorphic, hypautomorphic;
• Anhedral: a crystal that lacks any of its characteristic faces, completely malformed. Synonymous terms: allotriomorphic, xenomorphic.

 

Factors influencing 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); 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 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, i.e. pseudomorphous replacement. A classic example is tiger's eye quartz, crocidolite asbestos replaced by silica. While quartz typically forms prismatic (elongate, prism-like) crystals, in tiger's eye the original fibrous habit of crocidolite is preserved.

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Habit	Image	Description	Common example(s)
Acicular	Natrolite   Scolecite	Needle-like, slender, and end-tapered prisms growing in a radial/globular fashion.	natrolite, scolecite, yuanfuliite
Arborescent	Silver   Gold	Tree-like crystals growing similar to branches.	copper, gold, silver
Capillary/Filiform	Byssolite   Millerite	Hair-like or thread-like, extremely fine	byssolite, millerite
Colloform/Nodular/Tuberose	Agate   Sphalerite	Rounded, finely banded deposits with irregular concentric protuberances	agate, baryte, sphalerite
Concentric	Amethyst   Rhodocrosite	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	Copper   Romanechite	Root-like, branching in one or more direction from central point	copper, gold, romanechite, magnesite, silver
Druse/Encrustation	Celestine   Calcite	Aggregate of crystals coating a surface or cavity, usually found in geodes and some fossils	azurite, celestine, calcite, uvarovite, malachite, quartz
Fibrous/Asbestiform	Tremolite   Baryte	Extremely slender prisms forming muscle-like fibers	actinolite, asbestos, baryte, kyanite, gypsum, nitratine, stilbite, serpentine group
Foliated/Micaceous/Lamellar	Molybdenite   Biotite	Layered crystal planes, parting into thin sheets	biotite, hematite, muscovite, lepidolite, molybdenite
Granular	Uvarovite   Quartz	Aggregates of diminute anhedral crystals in matrix or other surface	andradite, bornite, scheelite, quartz, uvarovite
Hopper	Halite   Bismuth	Outer portions of cubes grow faster than inner portions, creating a concavity similar to that of a hopper	bismuth (artificial), halite, galena
Oolithic	Calcite   Calcite	Small cirumferences or grains (commonly flattened) that resemble eggs	aragonite, calcite
Pisolitic	Bauxite   Pisolite	Rounded concentric nodules often found in sedimentary rocks. Much larger than oolithic	aragonite, bauxite, calcite, pisolite
Platy/Tabular/Blocky	Baryte   Wulfenite	Flat, tablet-shaped, prominent pinnacoid	baryte, feldspar, topaz, vanadinite, wulfenite
Plumose	Aurichalcite   Okenite	Fine, feather-like scales	aurichalcite, okenite, mottramite
Radial/Radiating/Divergent	Atacamite   Pyrophyllite	Radiating outward from a central point without producing a star (crystals are generally separated and have different lengths).	aenigmatite, atacamite, epidote, pyrophyllite, stibnite
Reticulated	Cerussite   Rutile	Crystals forming triangular net-like intergrowths.	cerussite, rutile
Rosette/Lenticular	Baryte   Gypsum	Platy, radiating rose-like aggregate (also lens shaped crystals)	gypsum, baryte, calcite
Stalactitic	Chrysocolla   Calcite	Forming as stalactites or stalagmites; cylindrical or cone-shaped. Their cross-sections often reveal a "concentric" pattern	calcite, chalcedony, chrysocolla, goethite, malachite, romanechite
Stellate	Hematite   Wavellite	Star-like, radial fibers found inside spherical habits, such as mamillary or reniform.	hematite, pectolite, shattuckite, wavellite

Habit	Image	Description	Common example(s)
Amygdaloidal	Heulandite   Stilbite	Like embedded almonds	heulandite, stilbite, zircon
Hemimorphic	Hemimorphite   Olivine	Doubly terminated crystal with two differently shaped ends	elbaite, hemimorphite, olivine
Massive/Compact	Turquoise   Quartz	Shapeless, no distinctive external crystal shape	limonite, turquoise, cinnabar, quartz, realgar, lazurite
Sceptered	Amethyst   Baryte	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

Habit	Image	Description	Common example(s)
Cubic	Halite   Pyrite	Cube-shaped	fluorite, pyrite, galena, halite
Dodecahedral	Pyrite   Almandine	Dodecahedron-shaped, 12-sided. Central facet can vary.	garnet, pyrite
Enantiomorphic	Aragonite   Staurolite	Mirror-image habit (i.e. crystal twinning) and optical characteristics; right- and left-handed crystals	aragonite, gypsum, quartz, plagioclase, staurolite
Hexagonal	Vanadinite   Galena	Hexagonal prism (six-sided)	beryl, galena, quartz, hanksite, vanadinite
Icositetrahedral	Spessartine   Analcime	Icositetrahedron-shaped, 24-faced	analcime, spessartine
Octahedral	Spinel   Fluorite	Octahedron-shaped, square bipyramid (eight-sided)	diamond, fluorine, fluorite, magnetite, pyrite
Prismatic	Beryl   Tourmaline	Elongate, prism-like: may or not present well-developed crystal faces parallel to the vertical axis	beryl, tourmaline, vanadinite
Rhombohedral	Siderite   Rhodochrosite	Rhombohedron-shaped (six-faced rhombi)	calcite, magnesite, rhodochrosite, siderite
Scalenohedral	Calcite   Rhodochrosite	Scalenohedron-shaped, pointy ends	calcite, rhodochrosite, titanite
Tetrahedral	Sphalerite   Tetrahedrite	Tetrahedron-shaped, triangular pyramid (four-sided)	chalcopyrite, tetrahedrite, sphalerite, magnetite

Habit	Image	Description	Common example(s)
Botryoidal	Chalcedony   Calcite	Grape-like, large and small hemispherical masses, nearly differentiated/separated from each other	calcite, chalcedony, halite, plumbogummite, smithsonite
Globular	Gyrolite   Calcite	Isolated hemispheres or spheres	calcite, fluorite, gyrolite
Mammillary	Chalcedony   Hematite	Breast-like: surface formed by intersecting partial spherical shapes, larger version of botryoidal and/or reniform, also concentric layered aggregates.	chalcedony, hematite, malachite
Reniform	Malachite   Shattuckite	Irregular kidney-shaped spherical masses	cassiterite, chalcedony, chrysocolla, hematite, hemimorphite fluorite, goethite, greenockite, malachite, rhodochrosite, smithsonite, mottramite, wavellite

• Abnormal grain growth
• Grain growth
• Crystal structure

• Kostov, Ivan; Kostov, Ruslan I. (1999). Crystal Habits of Minerals. Sofia: Academic Publishing House "Prof. Marin Drinov". ISBN 9789546420602. OCLC 488807766.