OLIVINE
Olivine is a common mineral in many ultramafic igneous
rocks. It is magnesium iron silicate - (Mg,Fe)2SiO4.
“Olivine” actually refers to a continuous spectrum of chemistries between pure
magnesium silicate, Mg2SiO4 and pure iron silicate, Fe2SiO4.
Magnesium-rich olivine (forsterite) is more common than iron-rich
olivine (fayalite). Olivine is typically greenish-colored.
It has a hardness of 7, a conchoidal fracture, a glassy, nonmetallic luster,
and a white streak.
Forsterite olivine (each is ~10-15 mm across)