Cairngorm smoky quartz

John Ruskin called Scotland "one magnificent mineralogical specimen" in 1884, and the stone in your sporran is the proof.

Cairngorm quartz, usually just called cairngorm, is a yellow to dark-brown variety of smoky quartz tied to the Cairngorms of north-eastern Scotland. The name first meant gem-quality crystal collected on Cairn Gorm itself, on Ben Avon and on the mountains around them, and it later stretched to cover brown or yellow Scottish quartz generally. Matthew Forster Heddle catalogued it plainly as "Cairngorm, or Smoky Quartz", and recorded material going by that name from Sutherland and the Hebrides as well.

Chemically there is nothing exotic about it. Cairngorm is ordinary quartz, silicon dioxide, and the smoky colour is a radiation effect: traces of uranium and thorium in the surrounding granite irradiate the crystal across geological time and build colour centres inside it. The Grampian mountains that hold it are around 400 million years old.

Where the names get slippery is the gem trade. The lines between cairngorm, citrine, smoky quartz and morion rest on colour and custom rather than any sharp mineralogical boundary: yellow quartz tends to be called citrine, brown smoky quartz, and very dark brown to nearly black morion. Worse, yellow and brown quartz from other countries was historically sold as cairngorm, or as "false topaz", or simply as topaz, which is a different mineral altogether. And by eye alone, a genuine Cairngorm stone cannot be told from a foreign one.

It became one of Scotland's best-known ornamental stones from at least the eighteenth century, turning up in brooches and plaid brooches, seals and fob seals, buttons and kilt pins, the handles or mounts of dirks and sgian-dubhs, the lids of snuff mulls, and cases for jewellery, perfume and sewing equipment. A rich sherry-yellow was the colour most esteemed. Its origin and its association with Highland culture gave it an identity of its own even though a mineralogist would just write down smoky quartz.

National Museums Scotland holds a collection of cairngorm quartz that its curators describe as outstanding in Scotland and internationally important, tracing the material from the mountain through the hands of urban craftspeople and on to the people who wore and kept it. Much of the high ground is protected, so read the access rules before you take a hammer anywhere.