Extremely variable colour stone widespread in the world. Unfortunately his low hardness (4 from the Mohs scale) does not allow the use in the jewellery industry, except for necklaces or pendants. Although is soft, has a nice brilliancy. Quite often it react at long wave with a nice fluorescence likely due to Uranium and rare earths, sometimes to organic inclusions (hydrocarbons). Some material is thermo luminescent; some is phosphorescent.
Nevertheless is a fascinating stone; often zoned of various colours, while is rare to find flawless in big size.
This gem here has a good color change in the incandescent light and it comes from Ethiopia. Some small inclusions.