Inmineralogy,crystal habit is the characteristic external shape of an individualcrystal or aggregate of crystals. The habit of a crystal is dependent on itscrystallographic form and growth conditions, which generally creates irregularities due to limited space in thecrystallizing medium (commonly inrocks).[1][2]
Recognizing the habit can aid in mineral identification and description, as the crystal habit is an external representation of theinternal 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:
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 growthstriations. Minerals belonging to the samecrystal system do not necessarily exhibit the same habit. Some habits of a mineral are unique to its variety and locality: For example, while mostsapphires form elongate barrel-shaped crystals, those found inMontana form stouttabular crystals. Ordinarily, the latter habit is seen only inruby. 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 istiger's eye quartz, crocidoliteasbestos replaced bysilica. Whilequartz typically formsprismatic (elongate, prism-like) crystals, in tiger's eye the originalfibrous habit ofcrocidolite is preserved.
[3][better source needed][4][better source needed][5][better source needed][6]
| Habit | Image | Description | Common example(s) | ||
|---|---|---|---|---|---|
| Acicular |
| Needle-like, slender, and end-tapered prisms growing in a radial/globular fashion. | natrolite,scolecite,yuanfuliite | ||
| Arborescent |
| Tree-like crystals growing similar to branches. | copper,gold,silver | ||
| Capillary/Filiform |
| Hair-like or thread-like, extremely fine | byssolite,millerite | ||
| Colloform/Nodular/Tuberose |
| Rounded, finely banded deposits with irregular concentric protuberances | agate,baryte,sphalerite | ||
| Concentric |
| Circular ring aggregates around a center. This habit is found in cross-sections from reniform/mamillary habits, and also from elongated stalactites ofamethyst (quartz), malachites, rhodocrosite, and others | agate,quartz,malachite,rhodocrosite | ||
| Dendritic |
| Root-like, branching in one or more direction from central point | copper,gold,romanechite,magnesite,silver | ||
| Druse/Encrustation |
| Aggregate of crystals coating a surface or cavity, usually found ingeodes and somefossils | azurite,celestine,calcite,uvarovite,malachite,quartz | ||
| Fibrous/Asbestiform |
| Extremely slender prisms forming muscle-like fibers | actinolite,asbestos,baryte,kyanite,gypsum,nitratine,stilbite,serpentine group | ||
| Foliated/Micaceous/Lamellar |
| Layered crystal planes, parting into thin sheets | biotite,hematite,muscovite,lepidolite,molybdenite | ||
| Granular |
| Aggregates of diminute anhedral crystals inmatrix or other surface | andradite,bornite,scheelite,quartz,uvarovite | ||
| Hopper |
| Outer portions of cubes grow faster than inner portions, creating a concavity similar to that of ahopper | bismuth (artificial),halite,galena | ||
| Oolithic |
| Small spheres or grains (commonly flattened) that resemble eggs | aragonite,calcite | ||
| Pisolitic |
| Rounded concentric nodules often found in sedimentary rocks. Much larger than oolithic | aragonite,bauxite,calcite,pisolite | ||
| Platy/Tabular/Blocky |
| Flat, tablet-shaped, prominent pinnacoid | baryte,feldspar,topaz,vanadinite,wulfenite | ||
| Plumose |
| Fine, feather-like scales | aurichalcite,okenite,mottramite | ||
| Radial/Radiating/Divergent |
| Radiating outward from a central point without producing a star (crystals are generally separated and have different lengths). | aenigmatite,atacamite,epidote,pyrophyllite,stibnite | ||
| Reticulated |
| Crystals forming triangular net-like intergrowths. | cerussite,rutile | ||
| Rosette/Lenticular |
| Platy, radiating rose-like aggregate (also lens shaped crystals) | gypsum,baryte,calcite | ||
| Stalactitic |
| Forming asstalactites orstalagmites; cylindrical or cone-shaped. Their cross-sections often reveal a "concentric" pattern | calcite,chalcedony,chrysocolla,goethite,malachite,romanechite | ||
| Stellate |
| Star-like, radial fibers found inside spherical habits, such as mamillary or reniform. | hematite,pectolite,shattuckite,wavellite |
| Habit | Image | Description | Common example(s) | ||
|---|---|---|---|---|---|
| Amygdaloidal |
| Like embeddedalmonds | heulandite,stilbite,zircon | ||
| Hemimorphic |
| Doubly terminated crystal with two differently shaped ends | elbaite,hemimorphite,olivine | ||
| Massive/Compact |
| Shapeless, no distinctive external crystal shape | limonite,turquoise,cinnabar,quartz,realgar,lazurite | ||
| Sceptered |
| 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 |
| Cube-shaped | fluorite,pyrite,galena,halite | ||
| Dodecahedral |
| Dodecahedron-shaped, 12-sided. Central facet can vary. | garnet,pyrite | ||
| Enantiomorphic |
| Mirror-image habit (i.e.crystal twinning) and optical characteristics; right- and left-handed crystals | aragonite,gypsum,quartz,plagioclase,staurolite | ||
| Hexagonal |
| Hexagonal prism (six-sided) | beryl,galena,quartz,hanksite,vanadinite | ||
| Icositetrahedral |
| Icositetrahedron-shaped, 24-faced | analcime,spessartine | ||
| Octahedral |
| Octahedron-shaped, squarebipyramid (eight-sided) | diamond,fluorine,fluorite,magnetite,pyrite | ||
| Prismatic |
| Elongate, prism-like: may or not present well-developed crystal faces parallel to the vertical axis | beryl,tourmaline,vanadinite | ||
| Rhombohedral |
| Rhombohedron-shaped (six-faced rhombi) | calcite,magnesite,rhodochrosite,siderite | ||
| Scalenohedral |
| Scalenohedron-shaped, pointy ends | calcite,rhodochrosite,titanite | ||
| Tetrahedral |
| Tetrahedron-shaped, triangular pyramid (four-sided) | chalcopyrite,tetrahedrite,sphalerite,magnetite |
| Habit | Image | Description | Common example(s) | ||
|---|---|---|---|---|---|
| Botryoidal |
| Grape-like, large and small hemispherical masses, nearly differentiated/separated from each other | calcite,chalcedony,halite,plumbogummite,smithsonite | ||
| Globular |
| Isolated hemispheres or spheres | calcite,fluorite,gyrolite | ||
| Mammillary |
| Breast-like: surface formed by intersecting partial spherical shapes, larger version of botryoidal and/or reniform, also concentric layered aggregates. | chalcedony,hematite,malachite | ||
| Reniform |
| Irregularkidney-shaped spherical masses | cassiterite,chalcedony,chrysocolla,hematite,hemimorphitefluorite,goethite,greenockite,malachite,rhodochrosite,smithsonite,mottramite,wavellite |
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