Olivine

Olivine (abbreviated to Ol) is a common silicate mineral made of four elements only magnesium (Mg), iron (Fe), silicon (Si) and oxygen (O) – the latter two forming silica tetrahedra (SiO₄) – with the general formula (Mg,Fe)₂SiO₄.

Basic properties of olivine

• Color & appearance: Typically olive-green (hence the name), but can vary from yellow-green to brown. It often looks glassy and can form transparent crystals.
• Composition: It is a solid-solution series between two end members:
  • Forsterite (Mg₂SiO₄) → magnesium-rich olivine
  • Fayalite (Fe₂SiO₄) → iron-rich olivine
• Where it forms:
  • In igneous rocks like basalt, peridotite, and gabbro (major mineral of Earth’s upper mantle).
  • In some meteorites, especially stony (chondrites) and pallasites, making it important in meteoritics.
• Properties:
  • Hardness: ~6.5–7 on the Mohs scale
  • Density: relatively high due to iron and magnesium
  • Weathering: breaks down easily at Earth’s surface, altering to minerals like serpentine or iddingsite.

Olivine in meteorites

Olivine is a major constituent of many meteorite types, especially chondrites. In pallasites olivine crystals are embedded in a metallic iron-nickel matrix, creating a striking appearance. In planetary science, finding olivine in meteorites or on other planets can reveal information about mantle processes and planetary differentiation.