Bertrandite is a beryllium hydroxide mineral with composition: Be4Si2O7(OH)2. Bertrandite is a colorless to pale yellow orthorhombic mineral with a hardness of 6-7.
It is commonly found in beryllium rich pegmatites and is in part an alteration of beryl. Bertrandite often occurs as a pseudomorphic replacement of beryl. Associated minerals include beryl, phenakite , muscovite
It, with beryl, are ores of beryllium.
It was discovered near Nantes, France in 1883 and named after French , Emile Bertrand
One of the world's largest deposits of bertrandite is Spor Mountain, Thomas Range , Utah which is currently the source of most of the world's beryllium production.