Smoky quartz points collection box with 2-2.3 kilos of natural Smoky quartz from Corinto in Brazil.

Smoky quartz is a variety of quartz with a color ranging from smoky brown to almost black and is translucent. The darkest varieties are known as morion. It mainly occurs in cavities of intrusive and high-grade metamorphic rocks, while it is rare in sedimentary and effluent rocks. Notable sites include the Alps, Brazil, Russia, Mexico, India, Ireland, Zimbabwe, Afghanistan and the USA. The color of smoky quartz is caused by the presence of aluminum in the crystal lattice, in combination with ionizing radiation. Aluminum replaces silicon in the structure, creating the complex [AlO4-] instead of [SiO4]. During the growth of the crystal, small monovalent cations such as hydrogen, lithium or sodium are incorporated to compensate for the charge difference. Under the influence of ionizing radiation, an electron from the [AlO4-] complex moves to a cation, creating a color center. This process normally takes place below 50°C. At higher temperatures the color is broken down faster than it is formed. The source of the ionizing radiation is usually potassium-40 in the surrounding rock. Thus, the color of smoky quartz forms long after crystallization and can take millions of years, which explains why it is often found in granite. Above 200°C, smoky quartz loses its color. Irradiating clear quartz with X-rays or gamma rays almost always results in smoky quartz, a method used to convert colorless quartz into smoky quartz. In ancient times, the stone served as a warning to soldiers when it turned darker. Today, smoky quartz is still used in religious objects such as rosaries and crucifixes, and it is attributed to several medicinal properties.