Crystalline

Crystalline describes materials in which the constituent atoms or molecules are arranged in a highly ordered, repeating pattern that extends in all three spatial dimensions, forming a crystal lattice. This long-range order distinguishes crystalline solids from amorphous materials, where arrangement is more random.

The smallest repeating unit is the unit cell, and its arrangement defines the crystal lattice. Crystallography considers symmetry and lattice parameters; many crystals are polycrystalline, made of grains with different orientations, while single crystals have an uninterrupted lattice.

Crystals show anisotropy; properties vary with direction. They often have definite melting points and cleavage planes. They can be transparent to light and produce characteristic X-ray diffraction patterns that reveal their structure.

Common classes include ionic crystals (sodium chloride), covalent network crystals (diamond, quartz), metallic crystals, and molecular crystals (ice).

Crystallization from melt, solution, or vapor forms crystals through nucleation and growth. Real crystals contain defects and impurities that influence properties. Applications span electronics, optics, and pharmaceuticals, where crystal form affects solubility and bioavailability; X-ray crystallography is a central tool for structure determination.