Crystal

A crystal is a solid where the atoms formed a regular grid. Crystals grow at their surfaces, and different substance form different shaped crystals. Table salt forms crystals that are cubes. Diamonds are octahedrons.

Some crystal have unusual qualities, like piezoelectricity, where pressure triggers a small burst of electrons. Other crystals emit light, under pressure.

Modern electronics relies on "doping" pure crystals of semiconductor, making it possible allow or inhibit current flow.