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Scapolites are aluminosilicates that form in many different environments, including economic mineral deposits. Scapolites exist not only on Earth, but also in chondritic meteorites (Alexander et al., 1987) and may even exist on the surface of Mars (Swayze and Clark, 1990). Within this group is a Cl-rich end member known as marialite (Na3Al3Si9O24•NaCl). Little is known about the conditions at which marialite forms, especially the upper-pressure stability field. To determine this, experiments were conducted using a piston-cylinder press, multi-anvil press, and an X-ray diffractometer to analyze samples. The balanced reaction for marialite breakdown at high pressure is as follows: marialite = 3 jadeite + 3 quartz + halite. The marialite and jadeite components of the reaction needed to be synthesized using a piston-cylinder press. The quartz and halite components were readily sourced. A reversal mixture was created using the components of the balanced reaction. The boundary at upper pressures and temperatures for the growth of marialite was calculated based on thermochemical data from Almeida and Jenkins (2017, Amer. Min.). Multi-anvil experiments were conducted with the reversal mixture. The desired conditions for each run were determined based on data from other studies as well as the calculated boundary of marialite and jadeite + quartz + halite. Four multi-anvil experiments were conducted thus far with each one yielding a different result but indicating that growth of marialite occurs within 2.8 – 3.6 GPa at 1060 – 1300°C. Growths of marialite, jadeite, albite, and marialite occurred and all agreed with the calculated boundary and their confirmed respective boundaries. More experiments will be conducted to further narrow down the marialite upper-pressure stability field, but it appears that marialite can be a source of NaCl in the Earth’s upper mantle to depths of 85-110 km to help flux magma and economic mineral production.



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The Upper Pressure Stability Field of Marialite