Olivine

Chemical Formula : (Mg,Fe)₂SiO₄
Hardness : 6.5
Cleavage : Two, indistinct
Luster : Vitreous
Color : Olive-green, but end members are white (forsterite) and brwon to black (fayalite).
Streak : White
Density : 3.22 (fayalite) to 4.39 (forsterite)
Diagnostic Features and Trivia : Generic olivine is easily identified by its distinctive sugary textrue, sresembling a masses of fused green sugar crystals. Olivine has two end memebers: forsterite Mg₂SiO₄ and fayalite Mg₂SiO₄.
Crystal System and Habit : Orthorhombic; crystals are uncommon, usually forming in anhedral granular masses.
Twinning : None
Polymorphs : None
Index of Refraction : alpha=1.635-1.827; beta=1.651-1.869; gamma=1.670-1.879