Smoky Quartz

Smoky Quartz is a type of quartz crystal known for its black and brown shades. The crystal can be lightly colored or so deeply colored its opaque. Sometimes smoky quartz cooccurs with other kinds of quartz like amethyst and citrine

The crystals turn black when exposed to the natural radiation of decaying potassium in the stone around it turning the stone black. Sun exposure can bleach these crystals back to a clearer state. The BEST smoky or some people spell it smokey quartz is found by digging and has not been exposed to the sun before. 

Very black smoky quartz can be the result of radiation to deepen the color. Very deep black quartz should be questioned about treatments. Often this happens when it occurs with aquamarine and the miner irradiates the aquamarine to turn it more blue and it turns the smoky quartz pitch black. 

Like most black and dark stones, smoky quartz is known for it grounding properties.