Brown quartz includes quartz of a light brown or dark brown color, grayish brown "smoky" quartz, and the black variety called moron. Brown or smoky quartz from the Cairngorm Mountains of Scotland is called cairngorm. When irradiated, colorless quartz may change color to grayish brown, suggesting that brown quartz may have been formed by natural radiation within the ground. Brown quartz crystals are hexagonal prisms with pyramidal ends, in which inclusions of the mineral retile may be present.

Crystals weighing as much as 300kg (6501b) have been found in Brazil. Other localities include Madagascar, the Swiss Alps, and Colorado (USA). Australia and Spain.

Much of the smoky quartz on the market is in fact irradiated rock crystal. Brown quartz has been confused with andalusite, axinite, indorse. And brown tourmaline.