Crystal structure

From Wikinfo

In mineralogy a crystal structure is completely described by its unit cell lattice parameters, its space group symbol and the positions of the atoms that, when operated on by the essential rotational and translational symmetry operations, will generate entire contents within the unit cell.

A crystal structure is a concept fundamental to many areas of science and technology. Along with the unit cell lattice parameters, its space group symbol and the positions of the atoms entirely describe a crystal structure.

Unit cell

A unit cell is the orderly spatial arrangement of atoms in the molecular structure of a crystal.

The simplest and most symetrical, the isometric system, is represented by the cube. The other six systems, in order of decreasing symetry, are hexagonal, tetragonal, trigonal, orthorhombic, monoclinic and triclinic.

Bravais lattices

There are 14 basic arrangements of atoms in three dimensions, and all crystalline mineral structures recognised till now fit in one of these 14 arrangements.

The fourteen basic structure of minerals are the following:

• triclinic
• monoclinic (simple)
• monoclinic (centered)
• orthorhombic (simple)
• orthorhombic (base-centered)
• orthorhombic (body-centered)
• orthorhombic (face-centered)
• hexagonal
• rhombohedral
• tetragonal (simple)
• tetragonal (body-centered)
• isometric
• isometric (body-centered)
• isometric (face-centered)

The set of atomic positions (xi, yi, zi) are called the asymmetric unit.

See also

Crystal for a general definition and overview -- Crystallography -- Crystallographic defects

For more detailed information in specific technology applications see materials engineering, materials science, ceramics, metallurgy, or materials physics.

References

• Adapted from the Wikipedia article, "Crystal_structure" http://en.wikipedia.org/wiki/Crystal_structure, used under the GNU Free Documentation License