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Crystal system identification and geology

One of seven categories into which all crystalline minerals are classified based on the symmetry of their unit cell—the smallest repeating structural unit. The seven systems are: cubic isometric , tetragonal, orthorhombic, hexagonal, trigonal, monoclinic, and triclinic, defined by the relative lengths and angular relationships of the crystallographic axes. Crystal system determines the possible crystal forms and physical properties such as cleavage and optical behavior. Field: mineralogy. Example: Halite belongs to the cubic crystal system with three equal axes at 90°, which is why it always cleaves into cubes—its cubic symmetry is directly expressed in its cleavage geometry.. Related terms: Unit cell, Symmetry, Crystal habit, Crystallography.

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  • Previous: Cryptocrystalline — Describing a material composed of crystals so small that they cannot be resolved under a standard optical microscope, typically less than 1 micrometer.
  • Next: Cuprite — A copper oxide mineral Cu₂O with an isometric crystal system, a distinctive deep red color, and an adamantine to submetallic luster.

Sources, scope & corrections

These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.

Editorial owner
GeoMiner
Last updated
2026-03-30T15:19:41.970235+00:00
Review status
Published; not independently peer-reviewed
  • USGS Thesaurus — U.S. Geological Survey. Controlled earth-science terminology used to describe USGS information resources.
  • Glossary of Geologic Terms — U.S. National Park Service. Geologic definitions prepared by the NPS Geologic Resources Inventory.

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Common questions

What does Crystal system mean in geology?
One of seven categories into which all crystalline minerals are classified based on the symmetry of their unit cell—the smallest repeating structural unit. The seven systems are: cubic isometric , tetragonal, orthorhombic, hexagonal, trigonal, monoclinic, and triclinic, defined by the relative lengths and angular relationships of the crystallographic axes. Crystal system determines the possible crystal forms and physical properties such as cleavage and optical behavior.
What is an example of Crystal system?
Halite belongs to the cubic crystal system with three equal axes at 90°, which is why it always cleaves into cubes—its cubic symmetry is directly expressed in its cleavage geometry.
Which earth-science field uses the term Crystal system?
Crystal system is used in mineralogy.
Which terms are related to Crystal system?
Related terms in this reference are Unit cell, Symmetry, Crystal habit, Crystallography.

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