Fluid inclusions containing NaF have been extracted by healing quartz cracks at 700 °C and 1, 2, and 3 kbar. The aqueous NaF solutions belong to P–Q-type systems. They are characterized by the existence of two stable and one metastable immiscibility regions. Study of the inclusions showed that under these conditions, the fluid was in the heterogeneous state. The least dense phase detected in two-phase inclusions with the largest vapor bubble is an undersaturated aqueous solution. Its salt content points to a chemical interaction of NaF with quartz, which led to a change in the component composition of the system. As temperature grows, the highly viscous liquid of the inclusions segregates, and a new phase appears either around the vapor bubble or near the inclusion walls. At 3 kbar, one more type of inclusions with a vitreous phase forms, which shows anomalous behavior on heating. The phase changes in these inclusions can be interpreted only tentatively. Based on the data obtained, we suggest the existence of quasi-polymer compounds containing sodium hydrosilicates, in which OH groups are partly substituted by F. The results obtained are applied to study of natural processes involving fluids belonging to the P–Q-type systems.

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