Smoky quartz is the brown to nearly black member of the quartz family. Its colour forms when natural radiation from surrounding rock acts on tiny traces of aluminium in the crystal, a process taking place quietly underground over long ages. Scotland has a proud history with it: cairngorm, the smoky quartz of the Cairngorm mountains, is the national gem and stars in Highland dress jewellery. Other big sources include Brazil, Madagascar and the Swiss Alps. Colours run from gentle whisky tints to dramatic near-black.
With quartz's hardness of 7 and no cleavage, smoky quartz is an effortless everyday gem for rings, bracelets and bold pendants, and large clean stones cost pleasingly little. It is usually faceted, and darker stones look fantastic in modern designs.
Some material on the market is irradiated by people rather than by nature to deepen the colour, a stable practice that decent sellers disclose.
Keep it out of long, strong sunlight, which can slowly lighten it, and clean it with warm, soapy water.
All quartz siblings, each coloured by a different combination of trace elements and natural radiation.
