Smoky (Smokey) Quartz is a common, coarse-grained variety of the silica mineral Quartz. Its abudance causes it to be worth considerably less than citrine or amethyst. The color of smokey quartz ranges from nearly black through smoky brown. There is no distinct boundary exists between smoky and colorless Quartz. Irradiation and traces of aluminum built into its crystal lattice are what give punching fasteners factory the smoky quartz its color, but sometimes it is believed that it is the high energy cosmic radiation which causes its coloration and not the radiation from radioactive sources. Typically, the color of smoky quartz is much more homogeneous than that of amethyst. Quartz with deep colored or almost black, usually only occurs in igneous rocks. When heated to about 200°C, true smoky quartz will loose its color and when the crystal is irradiated with x- or gamma-rays, the color will occur again.

Certain smoky quartz is sensitive to ultraviolet light, it will turn pale if exposed to sunlight for a long time, but it is not as sensitive as amethyst. At certain locations smoky quartz shows zones of yellow or violet color along with smoky ones. These different colors might be found in different layers as “phantoms”.Smoky quartz is dichroic and when turned around an a-axis in polarized light, it shows a change of color from red-brown to yellow-brown. It’s still common practice to artificially irradiate colorless quartz, it is then sold as smoky quartz. People wont be able to tell just by looking at the crystal whether the source of the irradiation was natural or not, but dealers are obliged to clearly label that quartz accordingly although some of them don’t do that and get away with it.Usually smokey quartz is found in intrusive igneous and high grade metamorphic rocks, as these contain traces of radioactive elements.

Smoky quartz from volcanic rocks is more uncommon, here colorless quartz and amethyst dominate. Smoky quartz from sedimentary rocks is unusual because their content of radioactive elements is usually very low. Many “smoky” quartz reported from sedimentary rocks is actually not really smoky quartz, but quartz containing brown or black inclusions. Usually gangue quartz found at ore deposits is colorless or only slightly brown.