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Fayalite [abbr. Fa ]

Year of discovery: 1840 (Faial island (Fayal island), Portugal), 1914 (Japan)

Locality list: 81 localities of fayalite

• Fe₂SiO₄
• [Fe²⁺₂][SiO₄]^4-

• Class: Olivine group
• Class: Nesosilicate
• Variety: Knebelite (+Mn)
• Soluble in: HCl (Gel residue)
• Magnetism: Paramagnetic
• Alters by oxidation to Laihunite.
• Substitution pseudomorph: Replaced by Laihunite.
• Substitution pseudomorph: Replaced by clay minerals such as Nontronite. (Iddingsite)

• Fe => Zn: Willemite
• Fe => Mg: Forsterite (Series), Ringwoodite, Wadsleyite
• Fe => Be: Phenakite
• Fe => Ca: Calcio-olivine
• Fe => Ni: Liebenbergite
• Fe => Mn: Tephroite (Series)

• Fe₂ => CaMg: Monticellite
• Fe₂ => CaMn: Glaucochroite
• Fe₂ => CaFe: Kirschsteinite
• Fe₂ => LiAl: Eucryptite

• Fe²⁺₄ => Fe²⁺Fe³⁺₂: Laihunite

• Color: Brown, Greenish yellow
• Streak: Pale brown
• Luster: Vitreous
• Diaphaneity: Transparent-Translucent

• Habit: Short prismatic

• Cleavage: No
• Hardness: 7
• Density: 4.1

• System: Orthorhombic
• Group: mmm, Pbnm
• Lattice: a=4.8, b=10.4, c=6.1