Smoky Quartz

The colour of smoky quartz runs from a faint tea-tint to a near-opaque black, deepening like smoke through an otherwise clear crystal. The darkest, almost opaque form has its own name — morion — taken from a misreading of mormorion in Pliny the Elder's Natural History. Morion is also the standard German name for the whole variety.

The earliest documented use is curiously practical. In 12th-century China, flat panes of the stone were ground into sunglasses. The smoky tint cut the glare without colouring what the wearer saw.

The Cairngorm tradition

In Scotland the variety carries a place-name. Cairngorm is smoky quartz from the Cairngorm Mountains in the eastern Highlands, usually a smoky yellow-brown, sometimes greyish-brown. It became the signature Scottish ornamental stone. The yellow-brown crystals were set as centrepieces in plaid brooches. They also became the pommel stones for the sgian-dubh — the small black-handled knife tucked into the stocking of Highland dress. The form is still worn in brooches with Highland costume.

Why the colour exists

The smoky tint is not a pigment. Natural gamma rays from the surrounding rock activate colour centres — defects in the crystal lattice — clustered around traces of aluminium that have substituted for silicon. Pale alpine quartz can darken to deep brown over geological time. A colourless crystal sitting next to a uranium-rich granite eventually becomes smoky for the same reason.

Smoky quartz is cut today almost entirely for jewellery and ornamental use. The material is hard enough to take a high polish and common enough to stay inexpensive. The variety has become a popular gemstone in modern jewellery.

The largest commercial volumes are not crystals dug brown from the ground. Pale and colourless quartz, much of it from Brazil, is sent through gamma irradiation or electron-beam treatment and emerges as smoky, sometimes near-black morion. The resulting stones are cut and sold alongside the natural material; the treatment is permanent and leaves no residual radioactivity in the finished gem.

A related branch of the trade runs the other way. Heating smoky quartz bleaches it, sometimes through a yellow stage. The yellow material is then sold as citrine — a more expensive trade name than smoky quartz itself. Much of the inexpensive citrine on the market began as smoky quartz and was warmed to change colour.

In Scotland the natural Cairngorm stone continues its older role. It is still worn in brooches with Highland costume. The variety is also set as a decoration on kilt pins and the handles of sgian-dubh knives.