Cristalline

Cristalline describes a material or substance that possesses a regular, repeating arrangement of atoms or molecules extending in three dimensions to form a crystal lattice. In crystalline substances, the long-range order leads to well-defined external faces, distinct cleavage planes, a definite melting point, and properties that vary with direction (anisotropy). By contrast, amorphous materials lack such long-range order and do not exhibit sharp melting points or orderly cleavage.

The internal arrangement is described by a crystal lattice and a repeating unit called the unit cell. The lattice parameters and the arrangement of atoms within the unit cell determine the crystal system (cubic, tetragonal, orthorhombic, etc.) and the material’s symmetry. Crystallinity is routinely probed by X-ray diffraction, which yields sharp Bragg peaks for crystalline samples.

Crystalline materials form through crystallization: cooling of a melt, precipitation from a solution, or deposition from vapor. Nucleation seeds new crystals, and growth proceeds by the addition of atoms or molecules to crystallographic faces, often resulting in macroscopic crystals of well-defined shape.

Examples include minerals such as quartz (SiO2), halite (NaCl), and calcite (CaCO3); metals like copper and aluminum; and many organic compounds, including common pharmaceuticals. Crystalline form often affects properties such as stability, solubility, optical behavior, and mechanical strength.

See also crystallography, lattice, unit cell, polymorphism, amorphous solid.