BERTRANDITE (from the name of the French mineralogist E. Bertrand * EN: bertrandite; DE: Bertrandit; FR: bertrandite; ES: bertrandita; RU: бертрандит) is the mineral, diorthosilicate, Be4[Si2O7](OH)2. The content of the BeO is 34.5-41.6%. The impurities are Cu, Pb, Ag, Zn, Ge, B, and others. It crystallizes itself into the rhombic crystal systems. The structure is represented by the layers of the dual [SiO4]- and [BeO3ON]- tetrahedra, which are binded one with another. It forms the small plate-like crystals, radiating-beaming and sheaf-like aggregates, and grains. There are characteristic the twin crystals. It is colourless, white, less often pink, yellow; it is transparent. The cleavage is perfect. It is brittle. The hardness is 6. The density is 2540-2600 kilograms per cubic metre. It is widely distributed within the hydrothermal beryllium deposits (in association with fluorite, phenakite, quartz, feldspar, and so on) and beryllium-containing granitic pegmatites, as the product of the alteration of beryl (it associates itself with tourmaline, herderite).

It may be found within the quartz-wolframite-molybdenite veins, greisens and pegmatites of the nephelinic syenites. It is one of the main minerals of the beryllium ores. The major method of beneficiation is the flotation at the pH of 8.3 with the softened water, and also the combined processing, which is including the obtainment of the flotation concentrate from the poor ores, the mixing of this concentrate with the rich ore, soda, sodium fluoride, the subsequent agglomeration, roasting at 1700-1800 degrees Celsius, chemical leaching of beryllium with the obtainment of the hydroxide and other compounds of Be. Bertrandite is separated from beryl by the magnetic separation.