Quartz

Quartz is silicon dioxide arranged as a crystal. Its atoms form a regular, repeating pattern, which gives it six-sided crystals, a hardness of 7 on the Mohs scale and some useful electrical tricks. It's the second most common mineral in Earth's crust, after feldspar.

Natural quartz grows from silicon dioxide dissolved in hot water deep underground. As the water slowly cools, over thousands to millions of years, silica comes out of solution and adds onto growing crystals, layer by layer. Quartz veins and quartz-rich rock are mined as lumps for industry. Quartz for electronics is usually grown in factories instead. Seed crystals hang in steel pressure vessels filled with hot, alkaline water and crushed natural quartz, and over weeks to months they grow into large, flawless crystals.

Quartz is piezoelectric: squeeze it and it makes a voltage; apply a voltage and it flexes. A thin, precisely cut slice vibrates at one exact rate, which is the heart of a crystal oscillator. Lumps of natural quartz are also smelted with carbon to make metallurgical-grade silicon, the first step toward chips. Pierre and Jacques Curie discovered piezoelectricity in 1880.