Smoky Quartz

Smoky quartz is brown to black quartz, and it can be almost completely transparent or so dark it is nearly opaque. The photo shows two polished oval stones in dark brown, translucent, with lighter bands inside. According to Wikipedia, in some crystals the color is zoned, and sometimes it is darker near the edges.

Where does the smoke come from? According to Wikipedia and Geology.com, natural gamma radiation from the surrounding rock acts on tiny aluminium impurities inside the quartz and creates "color centers". Amethyst forms in a similar way, with iron instead of aluminium. And it can be undone: according to Wikipedia, if smoky quartz is heated above 200 to 300 °C or exposed to UV light, the color fades, and sometimes it turns a pale yellow that looks like citrine. Some heat-treated smoky quartz is sold as citrine.

Its best story comes from China. According to Wikipedia, as early as the 12th century, flat panes of smoky quartz were used there as sunglasses. And according to Geology.com, some were worn by judges in court, to hide their facial expressions. A 12th-century poker face.

In Scotland, smoky quartz is the national gem. According to Geology.com, it is called "cairngorm" there, after the Cairngorm Mountains, and according to Wikipedia, it decorates kilt pins and the handles of the small knife called the sgian-dubh. The very dark, almost black variety is called morion, and according to Wikipedia, that name comes from a misreading of the word mormorion in Pliny the Elder. According to Geology.com, in the Victorian era dark brown stones from the Mourne Mountains of Ireland were also used in mourning jewelry.

According to Geology.com, most of the smoky quartz used in jewelry today comes from Brazil, and also from Madagascar. It is common and relatively cheap, which makes it a favorite practice material for people learning to facet gems. If you get it wrong, it will not cost much.