Phenakite

Chemistry: Beryllium silicate.
Crystal system: Trigonal; short prismatic crystals; seldom large.
Color: Transparent; colorless, light yellow, pink, greenish blue (rare).
Hardness: 7.5
Cleavage: Indistinct: prismatic; fracture: conchoidal.
Specific gravity: 2.95
Refractive index: 1.65 – 1.67; Uniaxial positive; 0.016
Luster: Vitreous.
Dispersion: -
Dichroism: -
Occurrence: Africa, Brazil, Russia.

Notes
From the Greek word meaning to cheat or deceive; confused for quartz; rarely used in jewelry; one of the few crystal inclusions found in synthetic emerald; doubling; faceted.