1. A clear rock that looks like glass, especially quartz.
2. A crystalline substance that has semiconducting or piezoelectric properties and is used as an electronic component, or the electrical device using it.
3. Something that has the form of a crystal; for example, a frozen snowflake or a grain of salt.
4. A heavy transparent sparkling glass or household crystal glass objects made from heavy transparent sparkling glass.
5. Etymology: from Old English cristal, "clear ice, clear mineral", from Old French cristal, 12th century, Modern French crystal; from Latin crystallus, "crystal, ice"; from Greek krystallos, from kryos, "frost".

The Cambridge Encyclopedia of The English Language, 2nd edition; Cambridge University Press, New York, 2003.

The Stories of English; The Overlook Press; New York, 2004.

A structure formed by electrons trapped at a liquid helium surface at sufficiently high electron densities and low temperatures, in which the electrons occupy the points of a two-dimensional hexagonal lattice.

Divination by means of a crystal or other transparent body, especially a beryl: Little Sally sat at the table with a glass globe in front of her and tried to induce a psychic condition so that she could do some crystallomancy to impress her friends.

1. A crystal held together by the electric forces between ions, as for a chemical compound that is a salt; such as, sodium chloride.
2. A crystal in which the lattice-site occupants are charged ions held together primarily by their electrostatic interaction.
3. A crystal formed of an array of positive and negative ions held together by electrostatic forces.

An instrument for x-ray analysis of crystal structure and measuring wavelengths of X-rays and gamma rays, in which a homogeneous beam of X-rays is directed on the known face of a crystal and the reflected beam is detected in a suitably placed ionization chamber.

A nanostructured array of holes used as an optical semiconductor.

Just as electronic bandgaps (energy difference between a non-conductive state and the conductive state) prevent electrons from passing through, photonic crystals create photonic bandgaps that confine light.

This technology increases the efficiency in optical fibers and allows microscopic lasers to be built. It is also expected to be used in the construction of photonic circuits that can stand alone or be integrated into semiconductor circuits.

A crystal that exhibits the piezoelectric effect; such a crystal is used in electro-audio devices; such as, crystal microphones, speakers, and phonograph pickups.

Piezoelectricity has the function of certain crystals to generate a voltage in response to applied mechanical stress.

The result is reversible in that the piezoelectric crystals, subject to an externally applied voltage, can change shape by a minimal amount.

The change is in the degree of nanometers although there are useful applications; such as, the production and detection of sound, the generation of high voltages, electronic frequency generation, and the ultrafine focusing of optical assemblies.

A characteristic known as pyroelectricity, which is the ability of certain mineral crystals to generate electrical charges when heated, was determined as early as the 18th century, and was named by David Brewster in 1824.

In 1880, the brothers Pierre Curie and Jacques Curie predicted and demonstrated piezoelectricity using tinfoil, glue, wire, magnets, and a jeweler's saw.

They showed that crystals of tourmaline, quartz, topaz, cane sugar, and Rochelle salt (sodium potassium tartrate tetrahydrate) generate electrical polarization from mechanical stress.

Quartz and Rochelle salt exhibited the most piezoelectricity. There are twenty known natural crystal classes that exhibit direct piezoelectricity.

A crystal oscillator circuit whose oscillator output frequency can be varied or swept over a range of frequencies by varying a DC modulating voltage.