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Encyclopedia > Crystal habit

In mineralogy, shape and size give rise to descriptive terms applied to the typical appearance, or habit of crystals. Mineralogy is an earth science that involves the chemistry, crystal structure, and physical (including optical) properties of minerals. ... It has been suggested that crystallization processes be merged into this article or section. ...

Pyrite sun (or dollar) in laminated shale matrix. Between tightly spaced layers of shale, the aggregate was forced to grow in a laterally compressed, radiating manner. Under normal conditions, pyrite would form cubes or pyritohedrons.
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Pyrite sun (or dollar) in laminated shale matrix. Between tightly spaced layers of shale, the aggregate was forced to grow in a laterally compressed, radiating manner. Under normal conditions, pyrite would form cubes or pyritohedrons.

The many terms used by mineralogists to describe crystal habits are useful in communicating what specimens of a particular mineral often look like. Recognising 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 which are influenced by certain factors. Crystal habit may mislead the inexperienced as a mineral's crystal system can be hidden or disguised. Pyrite sun (or dollar) in laminated shale matrix. ... Pyrite sun (or dollar) in laminated shale matrix. ... Rose des Sables (Sand Rose), formed of gypsum crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ...


Factors influencing a crystal's habit include: a combination of two or more 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. It has been suggested that twin boundary be merged into this article or section. ... Sapphire (from Hebrew: ספּיר Sapir) is the single-crystal form of aluminium oxide (Al2O3), a mineral known as corundum. ... Official language(s) English Capital Helena Largest city Billings Area  Ranked 4th  - Total 147,165 sq. ... Ruby is a red gemstone, a variety of the mineral corundum (aluminium oxide) in which the color is caused mainly by chromium. ... Corundum is the crystalline form of aluminium oxide and one of the rock-forming minerals. ...


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. Polished tigers eye gemstone Tigers eye (also Tigers eye, Tiger eye) is a chatoyant gemstone that is usually yellow- to red-brown, with a silky luster. ... Quartz is amongst one of the most common minerals in the Earths continental crust. ... Amphibole (Hornblende) Amphibole defines an important group of dark-colored rock-forming inosilicate minerals composed of double chain SiO4 tetrahedra linked at the vertices and generally containing ions of iron and/ or magnesium in their structures. ... Fibrous asbestos on muscovite Asbestos Asbestos Asbestos (a misapplication of Latin: asbestos quicklime from Greek ἄσβεστος: a-, not; sbestos, extinguishable) describes any of a group of fibrous metamorphic minerals of the hydrous magnesium silicate variety. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ...


List of crystal habits

Habit: Description: Example:
Acicular Needle-like, slender and/or tapered Rutile in quartz
Amygdaloidal Almond-shaped Heulandite
Anhedral Poorly formed, distorted Olivine
Bladed Blade-like, slender and flattened Kyanite
Botryoidal or globular Grape-like, hemispherical masses Smithsonite
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
Dodecahedral Dodecahedron, 12-sided Garnet
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 Squashed, pinnacoids dominant over prisms Zircon
Euhedral Well-formed, undistorted 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: intersecting large rounded contours 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: all crystal faces parallel to c-axis Tourmaline
Pseudo-hexagonal Ostensibly hexagonal 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
Sphenoid Wedge-shaped Sphene
Stalactitic Forming as stalactites or stalagmites; cylindrical or cone-shaped Rhodochrosite
Stellate Star-like, radiating Pyrophyllite
Striated/striations Surface growth lines parallel or perpendicular to c-axis Chrysoberyl
Tabular or lamellar Flat, tablet-shaped, prominent pinnacoid Ruby
Wheat sheaf Aggregates resembling hand-reaped wheat sheaves Zeolites

  Results from FactBites:
 
Accelrys > Case Studies > Crystal Morphology Tools used in the Fight Against Malaria (305 words)
The prediction of crystal habit, the analysis of surface structure, and the design of additives is leading to pigments which show greatly improved performance expressed by a higher color strength, improved color shades, and a better color saturation.
The [011] crystal face was identified as a dominant crystal face and analyzed in detail.
This computational study demonstrated how the prediction of the crystal habit, the analysis of the surface structure and the design of additives is leading to pigments which show greatly improved performance expressed by a higher color strength, a more yellowish color shade and a better color saturation.
Mineral - New World Encyclopedia Preview (2156 words)
The crystal structure of a mineral is the orderly, geometric arrangement of atoms or ions in the mineral's internal structure.
There are 14 basic crystal lattice arrangements of atoms in three dimensions, and these are referred to as the 14 "Bravais lattices." Each of these lattices can be classified into one of the six "crystal systems." All currently recognized crystal structures fit into one Bravais lattice and one crystal system.
The typical, outward appearance of a mineral is called the "crystal habit." Some crystal habits are distinctive of certain minerals, but in most cases, a mineral exhibits a variety of habits that are influenced by the growth conditions of the crystals.
  More results at FactBites »


 

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