Class : Silicates
    Subclass : Nesosilicates
    Crystal system : Rhombohedral
    Chemistry : Be₂SiO₄
    Rarity : Uncommon

Phenakite is a beryllium silicate much rarer than beryl but which is found in the same type of occurrence as the latter : biotite micashists, and especially granitic pegmatites associated with topaz and/or chrysoberyl. It is a mineral that owes its name to the Greek phenax (misleading) because it looks like quartz when it is colorless. Phenakite is transparent to translucent and have a vitreous luster. Most often colorless, it can sometimes be yellowish, bluish or pinkish. Its crystals are flattened according to {001}, generally very rich in faces, or occurs in elongated hexagonal prisms, sometimes longitudinally striated and terminated by a rhombohedron. Phenakite is exceptionally used as beryllium ore, it is also cut for jewelry, but its lack of color makes it not very popular, its crystals are appreciated and sought after by mineral collectors.

In France, small crystals of phenakite are reported in the Alpine clefts of the Plan du Lac in Isere, but it has also been reported by Alfred Lacroix at Framont in Haute-Saône in a cavernous quartz penetrated with limonite, resulting from the decomposition of pyrite.

No fake inventoried for this species, however once cut the phenakite gemstones can be confused with the quartz whose optical properties are close.