Interactions of Mineral Surfaces with Water Vapor: A Method for Analyzing Surface Condensation on Halite Crystals

Condensation on mineral surfaces plays an important role in both natural and industrial environments, especially in the context of protecting sensitive geological formations. This paper presents the results of a new measurement method based on image analysis for non-invasive detection and classification of surface condensation on halite crystals. The presented method allows continuous monitoring of optical changes on the crystal surface in the visible light spectrum and also under natural (in situ) conditions. Based on the experiments carried out using halite samples from the Crystal Caves in the Wieliczka Salt Mine and literature data, four characteristic states of the crystal surface were distinguished. This classification was based on the values of relative humidity: (1) dry state (<65.0%), (2) quasi-static condensation (65.0%–75.5%), (3) transient unstable state (75.5%–77.0%), and (4) dynamic condensation (>77.0%), leading to intensive formation of brine solution on its surface. For the halite samples studied, the critical relative humidity (CRH) value was determined to be around 77.0%. The proposed measurement technique allows early detection of the presence of condensate and can be used as a qualitative classifier of the state of surface moisture, which allows automatic assessment of the risk of degradation. This method can find application in the protection of non-living nature reserves and cultural heritage sites, especially in the context of climate change and sustainable management of the underground environment.