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. Associated minerals include beryl, phenakite, herderite, tourmaline, muscovite, fluorite and quartz.<ref name=HBM/>
It, with beryl, are ores of beryllium.
It was discovered near Nantes, France in 1883 and named after French mineralogist, Emile Bertrand (1844–1909).<ref name=HBM/><ref name=Mindat/><ref name=Webmin/>
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.<ref name="USGS1">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="Full1968">Template:Cite book</ref>