Beryl comes in many forms, including some rarities such as the caesium rich variant in the photo, also known as Rosterite. While there is a caesium rich cousin of beryl called Pezzotaite (see http://on.fb.me/15DU72Z), Vorobyevite was deemed by those in charge of naming as not containing enough of it to be distinguished as a separate mineral. The name was applied to colourless material from the Urals mountains in Russia and rosy crystals from Madagascar until a stunning find of deep blue material in the Badakhshan province of Afghanistan. The blue crystals sit on a quartz matrix, and the piece measures 3.5 x 2.7 x 2.0 cm.
Image credit: Spirifer Minerals