Crystal System Identifier

Identify the crystal system of any mineral specimen by answering simple questions about crystallographic axes and angles. The decision-tree approach guides you through 7 crystal systems — cubic, hexagonal, trigonal, tetragonal, orthorhombic, monoclinic, and triclinic — with examples, symmetry elements, and visual axis diagrams for each result.

Identification

Identify Crystal System

Quick presets

Result

How to Use

1
Examine your specimen's axes
Look at the crystallographic axes of your mineral specimen. Determine whether all three axes are equal in length, two are equal, or all three differ. You can use a hand lens or reference images for help.
2
Check the angles between axes
Identify the angles between the crystallographic axes. Are all angles 90 degrees (right angles), or do some deviate? This narrows the possibilities significantly.
3
Read your crystal system result
The tool identifies one of 7 crystal systems based on your answers. Review the axis relationship, angle constraints, symmetry elements, and common mineral examples for your result.

FAQ

What is a crystal system?

A crystal system is one of seven categories that classify minerals based on the geometry of their unit cell — specifically the lengths of the three crystallographic axes (a, b, c) and the angles between them (alpha, beta, gamma). The seven systems, from highest to lowest symmetry, are cubic, hexagonal, trigonal, tetragonal, orthorhombic, monoclinic, and triclinic. Every crystalline mineral belongs to exactly one of these systems.

Are there 7 or 6 crystal systems?

Both counts are correct depending on convention. The International Union of Crystallography recognizes 7 crystal systems. However, some older textbooks list only 6 by merging trigonal into hexagonal, since both share a hexagonal lattice. Modern mineralogy treats trigonal as distinct because it has lower symmetry (3-fold vs 6-fold rotation axis). This tool uses the 7-system classification.

Can amorphous minerals have a crystal system?

No. Amorphous minerals like opal, obsidian, and natural glass lack the periodic internal atomic structure that defines a crystal system. They are technically mineraloids rather than true minerals. Some, like opal, contain tiny ordered domains (cristobalite spheres) but are classified as amorphous overall because they have no long-range crystal lattice.

What is polymorphism in minerals?

Polymorphism is the ability of a chemical compound to crystallize in more than one crystal system. For example, carbon forms diamond (cubic) and graphite (hexagonal). Calcium carbonate forms calcite (trigonal) and aragonite (orthorhombic). The same atoms arrange differently, producing minerals with identical chemistry but different physical properties — hardness, cleavage, density, and optical behavior all change with crystal structure.

How do I determine crystal system in the field?

In the field, look at crystal habit (external shape), cleavage directions, and optical properties. Cubic minerals often form cubes or octahedra (pyrite, fluorite). Hexagonal/trigonal minerals show 6-fold or 3-fold symmetry (quartz prisms, calcite rhombs). Tetragonal crystals are elongated squares (zircon). For ambiguous cases, a hand lens to count symmetry elements or a polarizing filter to check optical behavior helps confirm the system.

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