Magnesite forms as an economic mineral in ultramafic rocks through the process of carbonation, where magnesium-rich minerals (e.g., olivine or serpentine) react with carbon dioxide-bearing fluids. This typically occurs under low to moderate temperatures (50–200°C) and high CO₂ concentrations in a hydrous environment. Magnesite deposition is often associated with hydrothermal systems, where fluids percolate through ultramafic rocks, promoting the transformation of magnesium silicates into carbonates. Tectonic settings like mid-ocean ridges, subduction zones, or ophiolite complexes provide the necessary fluid-rock interactions for its formation. Economic deposits are often linked to large-scale fault systems that enhance fluid circulation and carbonation reactions.