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. Recently good material has been found in China of various colors: green,blue,purple and yellow . This stone has been cut in China and the type of cutting is called “concave cut”, very bright with a good luster .Natural untreated.