Bertrandite is more commonly called Tiffany Stone. It has also been called Purple Passion and Icecream Opal. Tiffany stone is a common opal. Tiffany stone is generally opaque but can be translucent. Tiffany stone gets it's wonderful purple colors from Fluorite.
Tiffany Stone comes from the Brush Wellman Beryllium mine in Utah. The mine is no longer open for collecting and all of this beautiful material is now ground up as beryllium ore.
Tiffany stone can have some uneven hardness (undercutting). However most Tiffany stone cuts easily and takes a fine polish. with a mohs hardness of 5 to 6.