Vitruvian Amber

A semi-precious stone found only on the planet Nix, and one of the planet's only significant exports. The Amber is partly mineral, combined with fossilised remnants of pre-colonisation bacteria and fungi. These contain complex enzymes which undergo a reaction under strong light; then glow slightly as they decompose back to their stable form. On Nix, a chunk of Vitruvian Amber will glow about as brightly as a small candle, illuminating rooms well enough to prevent you tripping in the dark, and then recharge from sunlight during the day.

On other worlds, the Amber glows more brightly, and may display exotic colours such as red and green (rather that the natural blue-gold usually seen on Nix) as the enzymes are raised to higher energy states by the long-UV radiation (which is filtered out on Nix by the unusual composition of the stratospheric layers). However, this higher energy also tends to destroy the amber, which becomes cloudy over a period of a few months.