Smoky Quartz from Jesseville, Hot Springs, Arkansas, U.S.A.

Smoky quartz is a variety of quartz. The colour is smoky brown to almost black, translucent. Very dark varieties are called morion. Smoky quartz is most common in cavities in intrusion rocks and high-grade metamorphic rocks. Smoky quartz is rare in sedimentary rocks and extrusive rocks. Locations include the Alps, Brazil, Russia, Mexico, India, Ireland, Zimbabwe, Afghanistan and the U.S.A. The combination of aluminium in the crystal lattice and ionising radiation causes the colour of smoky quartz. 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 colour centres occurs more quickly than their creation. The source of the ionising radiation is usually potassium-40, the surrounding rock. The colour of smoky quartz therefore develops long after the crystals have formed, and it can take 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. Radiating clear quartz (rock crystal) with X-rays or gamma radiation almost always produces smoky quartz. This method is also used to make smoky quartz from colourless quartz. In ancient times, this stone warned soldiers in battle if it turned dark. Smoky quartz is still used today for rosaries and crucifixes. A number of 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. More information