FLUORITE
Fluorite can look very much like amethyst, except
the purple colour is much more likely to be in distinct bands through the stone,
alternating with clear areas. It can, however contain yellow or green, which never
occur
in amethyst. 
Also known as fluorspar, it is found in Derbyshire in England, where it is known as Blue John. It is also found in other parts of the world in a wider range of colours. It is often carved in Hong Kong and China.
The