Darker than many other quartzes, smoky quartz ranges from a yellowish-brown to a dark brown that can even appear grey or black; reddish and orangish smoky quartz are popular in cut gems and jewelry. The colors of this quartz originate from natural radiation in the earth which activates color centers around aluminum inside the crystal. The darker hue, combined with the hazy transparency of the quartz, gives off an aura of steadiness, stability, and power.