Smoky Quartz Crystal 61 kilos (91 cm x 30 cm) (100% natural, not fired) from Arkansas, in the U.S.A.

Smoky quartz is various quartz. The colour of smoky quartz ranges from smoky brown to almost black and is translucent. We call the very dark varieties "morion." Smoky quartz is most common in cavities in intrusive rocks and high-grade metamorphic rocks. In sedimentary rocks and effusive rocks, smoky quartz is rare. Localities include the Alps, Brazil, Russia, Mexico, India, Ireland, Zimbabwe, Afghanistan and the USA. Ionising radiation in combination with aluminium in the crystal lattice causes the colour of smoky quartz to change. The aluminium replaces the silicon in the crystal structure, whereby the complex [AlO₄⁻] is formed instead of [SiO₄]. To compensate for the resulting charge difference, small monovalent cations of, for example, hydrogen, lithium or sodium are simultaneously incorporated into the crystal structure during the growth of the crystal. Under the influence of ionising radiation, the electron of the [AlO₄⁻] complex moves to a cation, and a colour centre is created. This process normally only takes place below 50°C. At higher temperatures, the breakdown of the coloured centres occurs faster than their creation. The source of the ionising radiation is usually potassium-40, the surrounding rock. Therefore, the formation of smoky quartz's colour occurs long after the crystals have formed, often taking several million years. This phenomenon also accounts for the formation of most smoky quartz in feldspar-rich rocks, including granite. When heated above 200°C, the smoky quartz will lose its colour. Irradiating clear quartz (rock crystal) with X-rays or gamma radiation almost always produces smoky quartz. We also use this method to transform colourless quartz into smoky quartz. In ancient times, this stone warned soldiers in battle if it turned dark. Smoky quartz is still used today for rosaries and crucifixes. Several medicinal properties are attributed to smoky quartz; it is said to help with digestive complaints, stress, grief and a desire to have children. According to various literature, the mineral belongs to the zodiac sign Libra.