A homogenous solid formed by a repeating, three-dimensional pattern of atoms, ions, or molecules and having smooth external surfaces with characteristic angles between them. Crystals can occur in many sizes and shapes. ◇ The particular arrangement in space of these atoms, molecules, or ions, and the way in which they are joined, is called a crystal lattice. There are seven crystal groups or systems. Each is defined on the basis of the geometrical arrangement of the crystal lattice.
A natural or synthetic material, such as quartz or ceramic, that consists of such crystals. When subjected to mechanical stresses, crystalline materials can generate an electric charge or, when subjected to an electric field, they can generate mechanical vibrations in what is known as the piezoelectric effect.
An electrical device, such as an oscillator or a diode used for detecting radio signals, made of such a material.