Smoky Quartz
Smoky quartz is a variety of QUARTZ. The brown, black or smoky gray color is due to exposure to radiation - either natural or artificial.
Smoky quartz is used as an inexpensive gemstone, and is a popular material for carved objects such as spheres, figurines, pyramids, etc.
Chemistry: Silicon dioxide (SiO2) ♦ Class: Quartz ♦ Moh's hardness: 7 ♦ Crystal system: Trigonal, hexagonal prisms ♦ Color: Brown to black, smoky gray ♦ Transparency: Transparent ♦ Cleavage: None ♦ Fracture: Conchoidal, very brittle ♦ Localities: USA, Brazil, Madagascar, Russia, Scotland, Switzerland, Ukraine