SEDIMENTARY MAGNESITE FORMATION THROUGH TEMPERATURE AND PH FLUCTUATIONS

Incorporating magnesium into the carbonate structure is difficult at low temperatures. However, Veitsch-type anhydrous magnesites (MgCO₃) are found in evaporative environments without the typical hydrothermal conditions associated with magnesite formation. To address the disconnect, this study refined a temperature and pH cycling method to achieve up to 91 mol% MgCO₃ of (Mg,Ca)CO₃ carbonates without exceeding 40 °C. Individual parameters were tested to develop a novel simultaneous growth and replacement mechanism for magnesite formation. The experimental conditions ideal for magnesite growth match very well with an evaporative/lagoonal/playa geologic setting: small thermal mass for daily temperature swings, algal mass for pH control, and a solution highly concentrated in Mg²⁺ with high Mg:Ca ratios. Additionally, this study suggests the inclusion of dissolved silica in the system may play an important, but previously unacknowledged, catalytic role in the development of magnesium bearing carbonates. Finally, a high mol% MgCO₃ carbonate precursor, such as the one produced in this study, is needed for the diagenetic alteration towards pure magnesite.