Quartz

Quartz or PJX1-8 is a crystalline mineral abundant on the planet Earth but rarer elsewhere. (DW: The Pirate Planet)

Quartz is frequently used for decorative purposes but its electrical properties make it valuable in electronics. It is often used as a component of clocks. (DW: The Sontaran Experiment) Quartz arranged in regular patterns within rock can form circuit boards. (NSA: The Deviant Strain)

Notable Uses

 * Quartz eyes were set from behind in the faces of the Cave of Five Hundred Eyes in China. They reflected light to give the appearance of movement but could also be removed to view through. (DW: Marco Polo)
 * The first Dalek Emperor, upon taking the title, ordered the gathering of quartz for the creation of his special casing. (TV21: Genesis of Evil)