gems, beryl, Mozambique, Maria, alkali-carbonic solution, emerald, fluid inclusions, nahcolite

The compositions of fluid inclusions in emerald and quartz from the Maria deposit in Mozambique were investigated using microthermometric and Raman microprobe techniques. The inclusions in emerald belong to the Na–Ca–Mg–(HCO₃)⁻–(CO₃)²⁻–Cl–H₂O system and are saturated carbonic acid brines. Nahcolite is the primary daughter mineral phase observed, with average concentrations of 25 wt.% nahcolite and 5 wt.% NaCl. Additional daughter phases identified include Mg-calcite, magnesite, calcite, and aragonite. Many fluid inclusions show a necked-down morphology, with groups of nahcolite crystals often comprising up to ~50 vol.% of these inclusions. Zones rich in fluid inclusions containing numerous birefringent solids appear to be characteristic of emeralds from the Maria deposit. Estimated conditions for emerald formation are between 400 and 500 °C and pressures of 3 to 4 kbar.