Triclinic crystal system

The triclinic (or anorthic) crystal system is one of the 7 crystal systems in crystallography. A crystal system is a geometric classification system used to describe the arrangement of atoms in a crystalline solid. In the triclinic system, the crystal is described by three basis vectors of unequal length, similar to the orthorhombic system. However, the angles between these vectors are all different and none of them are equal to 90 degrees.

Characteristics

Triclinic crystal systems are characterized by the following properties:

• Three unequal lattice vectors (a, b, and c)
• Angles between the vectors are all different (α, β, and γ) and none are equal to 90 degrees
• The simplest triclinic lattice is the primitive triclinic lattice (P), which has lattice points at the corners of the unit cell
• Triclinic systems have the lowest symmetry among the seven crystal systems, with only two point groups (1 and -1)

Bravais Lattices

There is only one Bravais lattice in the triclinic crystal system, the primitive triclinic lattice (P). In this lattice, there is only one lattice point per unit cell, located at the corners.

Point Groups

Triclinic crystal systems have two point groups:

Triclinic Pinacoidal (point group 1): This group has no symmetry operations other than the identity operation. Triclinic Pedial (point group -1): This group has inversion symmetry (center of symmetry) as the only operation.

Examples

Some minerals that crystallize in the triclinic crystal system include:

• Microcline (a type of potassium feldspar)
• Axinite (a group of calcium aluminum borosilicate minerals)
• Rhodonite (a manganese inosilicate)
• Turquoise (a hydrous phosphate of copper and aluminum)

Comparison with other crystal systems

The triclinic system is unique among the seven crystal systems in that it has the least symmetry and the most general set of lattice parameters. In comparison, the other six crystal systems have more constraints on the lengths and angles of their lattice vectors, resulting in higher symmetry.

See also

• Crystallography
• Crystal system
• Orthorhombic crystal system
• Monoclinic crystal system

Triclinic crystal system Resources
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