Fayalite is a extremely rare member of the Olivine group of minerals that includes Dunilite, Fayalite, Forsterite and Peridot (Olivine)although Peridot is not recognized as a mineral that is split. Fayalite and Forsterite are simply known as Olivine. Fayalite is the iron rich person in the series and Forsterite could be the magnesium member that is rich. Due to its iron content, Fayalite has a higher index of refraction, is heavier, and often has a darker color. Otherwise, they’ve been difficult to distinguish and virtually all specimens of the two minerals contain both magnesium and iron. The color that is best of Peridot has an iron content less than 15% and includes traces of nickel and chromium.

The treasure selection of Forsterite is frequently known as the bright green Peridot. But a discover that is recent of Forsterite in Mogok, Myanmar (Burma) has apparently brought a new variety of gemstone towards the market. Colorless Forsterite gems were virtually uncommon previous to this find.

Fayalite is found at several locations around the entire world and also in many meteorites that are iron-nickel. Fayalite was even found at the Sea of Tranquility on the Moon in lunar basalt by the Apollo 11 and 14 mission astronauts.

Category: Nesosilicate
Formula: Fe2SiO4
Crystallography: Orthorhombic – Dipyramidal
Crystal Habit: Crystals are thick to thin, tabular, typically with wedge-shaped terminations, producing eight-sided cross sections. Commonly granular, compact, or massive.
Twinning: On [100]; also on [031], as trillings.


Cleavage: [010] Imperfect, [100] Imperfect
Fracture: Conchoidal
Tenacity: Brittle
Hardness (Mohs): 6.5 – 7.0
Density: 4.392 (g/cm3)
Luminescence: None
Radioactivity: Not Radioactive


Color: Greenish Yellow, Yellow-Brown, Brown, rarely Colorless
Transparency: Transparent, Translucent
Luster: Vitreous, Greasy
Refractive Index: 1.731 – 1.875  Biaxial ( – )
Birefringence: 0.042 – 0.051
Dispersion: Weak; r > v
Pleochroism: Faint; X = Z = pale yellow; Y = yellow-orange, reddish brown.