Bertrandite

Bertrandite is a beryllium sorosilicate 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. It, with beryl, are ores of beryllium.

It was discovered near Nantes, France in 1883 and named for the French mineralogist, Léon Bertrand.