Mineral or Crystal habits are descriptions of the shapes and aggregates that a certain mineral is likely to form. Often this is the most important characteristic to examine when identifying a mineral. Although most minerals do have different forms, they are sometimes quite distinct and common only to one or even just a few minerals. Many collectors strive to collect mineral specimens of certain typical and abnormal habits.
There are basically two major divisions to keep in mind when discussing crystal habits. First, there are crystallographic forms whose names often separate the true Rock Hounds from the amateurs. These crystal forms are controlled by the structure and therefore the symmetry of the crystal. Secondly there are more descriptive terms that quickly portray the character of the crystal or aggregate crystals. The shape and character of the aggregate may be just as distinctive as an individual crystal's shape.
The many different crystallographic forms can look rather complicated to novice collectors. However, understanding them can greatly increase the chance of correctly identifying minerals and appreciating the specimens that belong to your collection. There are either open forms or closed forms.
- Acicular - Occurs as needle-like crystals.
- Aggregates - Made of numerous individual crystals or clusters.
- Amorphous - No crystalline form or imitative shape.
- Anhedral Grains - Granular minerals without the expression of crystal shapes
- Arborescent - "Tree like" growths of branched systems (e.g. silver).
- Bladed - Aggregates of thin lath-like crystals (e.g. kyanite).
- Blocky - Crystal shape tends to be equant (e.g. feldspars).
- Blocky (Rhombohedral) - Crystal shape resembles rhomohedrons.
- Botryoidal - "Grape-like" rounded forms (e.g. malachite).
- Capillary - Very slender and long, like a thread or hair (e.g. millerite).
- Cleaveable - Easily cleaved into fragments.
- Cog-wheel - Generally six sided twinned crystals forming Cog-Wheel shapes
- Colloform - Forming from a gel or colloidal mass.
- Columnar - Forms columns
- Comb - Drusy layers deposited on top of each other to produce a toothed structure (e.g. amethyst)
- Compact - Occurs as a compact mass.
- Concretionary - Rounded massive fine-grained materials.
- Cruciform - Twinned tabular crystals with a cross-like outline.
- Cryptocrystalline - Occurs as crystals too small to distinguish with the naked eye.
- Crystalline (Coarse) - Occurs as well-formed coarse sized crystals.
- Crystalline (Fine) - Occurs as well-formed fine sized crystals.
- Crystalline (Poor) - Occurs primarily as crudely formed crystals.
- Cubic Crystals - Occurs as cubic shaped crystals.
- Cylindrical - Shaped like a cylinder.
- Deliquescent - Crystals absorb water from the air and melt or otherwise deteriorate.
- Dendritic - Branching "tree-like" growths of great complexity (e.g. pyrolusite).
- Disseminated - Occurs in small, distinct particles dispersed in matrix.
- Divergent - Crystals radiate from a center without producing stellar forms.
- Druse - Crystal growth in a cavity which results in numerous crystal tipped surfaces.
- Earthy - Dull, clay-like texture with no visible crystalline affinities, (e.g. howlite).
- Efflorescences - Crystals covering matrix, generally produced from transpiro-evaporation.
- Encrustations - Forms crust-like aggregates on matrix.
- Euhedral Crystals - Occurs as well-formed crystals showing good external form.
- Fan Shaped - Occurs as radiating crystals shaped like a fan.
- Fibrous - Crystals made up of fibers.
- Flakes - Flat, thin crystals or aggregates.
- Foliated - Two dimensional platy forms.
- Friable - Loosley cohesive material that granulates with your fingers.
- Globular - Spherical, or nearly so, rounded forms (e.g. wavellite).
- Granular - Generally occurs as anhedral to subhedral crystals in matrix.
- Hexagonal - Six-sided crystal shape in cross-section or habit.
- Inclusions - Generally found as inclusions in other minerals.
- Indistinct - Crystals or grains are unremarkable or poorly formed.
Anhedral to subhedral crystals.
- Intergrown Crystals - Occurs as intergrown crystalline aggregates
- Irregular Grains - Occurs as splotchy, anhedral crystals forming inclusions in other minerals or rocks.
- Lamellar - Thin laminae producing a lamellar structure.
- Lath - Shaped like a small, thin plaster lath, tabular (rectangular) in shape.
- Liquid - Occurs as a liquid at room temperatures.
- Mammillary - Larger "breast-like" rounded forms resembling botryoidal (e.g. malachite).
- Massive - Uniformly indistinguishable crystals forming large masses.
- Massive (Fibrous) - Distinctly fibrous fine-grained forms.
- Massive (Granular) - Common texture observed in granite and other igneous rock.
- Massive (Lamellar) - Distinctly foliated fine-grained forms.
- Metamict - Mineral originally crystalline, now amorphous due to radiation damage.
- Micaceous - Platy texture with "flexible" plates.
- Microscopic Crystals - Crystals visible only with microscopes.
- Mossy - Like moss in form or appearance.
- Nodular - Tuberose forms having irregular protuberances over the surface.
- Nuggets - Irregular lumps produced by stream transport of malleable metals.
- Octahedral Crystals - Occurs as octahedral shaped crystals.
- Oolitic - <3mm rounded spherical grains.
- Pistolitic - >3mm rounded spherical grains.
- Platy - Sheet forms (e.g. micas).
- Plumose - "Mica-like" minerals forming aggregates of plume-like forms.
- Porcelainous - Fine-grained, translucent massive material like broken china
- Powdery - Forms a loose, poorly-coherent pulverulent mass.
- Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline).
- Pseudo Cubic - Crystals show a cubic outline.
- Pseudo Hexagonal - Crystals show a hexagonal outline.
- Pseudo Octohedral - Crystals show an octohedral outline.
- Pseudo Orthorhombic - Crystals show an orthorhombic shape.
- Pseudo Rhombohedral - Crystals show a rhombohedral outline.
- Pseudo Tetragonal - Crystals show a tetragonal shape.
- Pseudomorphous - Occurs in the form of another mineral.
- Pulverulent - Forms a loose, poorly-coherent powdery mass.
- Pyramidal - Crystals are shaped like pyramids.
- Radial - Crystals radiate from a center without producing stellar forms (e.g. stibnite)
- Reniform - "Kidney like" in shape (e.g. hematite).
- Reticulate - Fibers or columns cross in "Net-like" crystalline growths (e.g. cerrusite).
- Rhombohedral Crystals - Occurs as well-formed crystals showing rhobohedral crystals.
- Rosette - Bundled tabular aggregates resembling rose flower petals.
- Scaly - Morphology like fish scales.
- Skeletal - Crystals form crude outlines with missing faces.
- Spherical - Spherical, rounded aggregates.
- Square - Occurs as square crystals in shape or outline.
- Stalactitic - Shaped like pendant columns as stalactites or stalagmites (e.g. calcite).
- Stellate - Occurs as spherical, radial aggregates radiating from a "star" like point.
- Striated - Parallel lines on crystal surface or cleavage face.
- Subhedral Crystals - Occurs as crystals which tend to exhibit a recognizable crystal shape.
- Sugary - Granular texture formed from small, anhedral to subhedral grains forming massive rock.
(Aplitic texture).
- Tabular - Form dimensions are thin in one direction.
- Tarnishes - Freshly fractured surfaces form a surface oxidation film
- Tastes Bitter - Bitter taste from water soluble Mg or Ca compounds.
- Thin - Flat dimensioned crystals.
- Triangular Crystals - Occurs as triangular shaped crystals.
- Twinning Common - Crystals are usually twinned.
- Unknown - Unknown.
- Very Soluble - Material dissolves readily in water leaving no residue.
- Water Soluble - Water soluble mineral.
- Waxy - Looks like candle wax.
- Wedge shaped - Crystals shaped like a wedge.
- Wheat Sheaf - Bundle shaped aggregates resembling wheat sheafs after hand reaping wheat.
