bertrandite
noun
ber·trand·ite
ˈbər-trən-ˌdīt
plural -s
: a mineral Be4Si2O7(OH)2 consisting of a beryllium silicate occurring in hard colorless or pale-yellow prismatic crystals (hardness 6–7, specific gravity 2.59–2.60)
Word History
Etymology
French, from E. Bertrand, 19th century Frenchman who first described it + French -ite