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The abandoned gypsum quarry at Dingwall, in Canada, is a unique place with a peculiar “living” landscape created by expansive hydration of anhydrite process actively operating in the weathering zone at the quarry bottom. It causes a rapid volume increase of the rocks and the formation of the unique domed and tepee-like hydration landforms (several meters in length and up to 2.09 m high) with internal hydration caves (swelling caves, German: Quellungshöhlen). The quarry also shows some rare evaporite minerals, sulphate karst, spheroidal weathering of anhydrite and the other phenomena. Several steps of geoconservation strategy are described to promote Dingwall quarry as a geosite and a geodiversity site: inventory, quantitative assessment, conservation, interpretation, promotion and monitoring. The performed inventory describes the elements of the geoheritage. The quantitative assessment of the site, made according to the method by Brilha (Geoheritage 8:119–134, 2016), was based on the four aspects: scientific value, potential educational use, potential tourist use and the rate of destruction. For showing the geological heritage, the plan of the site was prepared, with paths for visitors, attendant infrastructure, thematic interpretation panels and plates with QR codes. As a part of the promotion, application of the Internet with already operating sites (e.g. hydrationcave.com) is proposed. In turn, monitoring, with measurements of benchmarks and photographic and photogrammetric documentation, will ensure the proper functioning of the site after establishing it as a geosite and a geodiversity site.

In the Dingwall gypsum quarry in Nova Scotia, Canada, operating in 1933–1955, the bedrock anhydrite deposits of the Carboniferous Windsor Group have been uncovered from beneath the secondary gypsum beds of the extracted raw material. The anhydrite has been subjected to weathering undergoing hydration (gypsification), transforming into secondary gypsum due to contact with water of meteoric derivation. The ongoing gypsification is associated with a volume increase and deformation of the quarry bottom. The surface layer of the rocks is locally split from the substrate and raised, forming spectacular hydration relief. It shows numerous domes, ridges and tepee structures with empty internal chambers, some of which represent unique hydration caves (swelling caves, Quellungshöhlen). The petrographic structure of the weathering zone has been revealed by macro- and microscopic observations. It was recognized that gypsification commonly starts from a developing network of tiny fractures penetrating massive anhydrite. The gypsification advances from the fractures towards the interior of the anhydrite rocks, which are subdivided into blocks or nodules similar to corestones. Characteristic zones can be recognized at the contact of the anhydrite and the secondary gypsum: (1) massive and/or microporous anhydrite, (2) anhydrite penetrated by tiny gypsum veinlets separating the disturbed crystals and their fragments (commonly along cleavage planes), (3) gypsum with scattered anhydrite relics, and (4) secondary gypsum. The secondary gypsum crystals grow both by replacement and displacement, and also as cement. Displacive growth, evidenced by abundant deformation of the fragmented anhydrite crystals, is the direct cause of the volume increase. Crystallization pressure exerted by gypsum growth is thought to be the main factor generating volume increase and, consequently, also the formation of new fractures allowing water access to “fresh” massive anhydrite and thus accelerating its further hydration. The expansive hydration is taking place within temperature range from 0 to ~30 °C in which the solubility of gypsum is lower than that of anhydrite. In such conditions, dissolving anhydrite yields a solution supersaturated with gypsum and the dissolution of anhydrite is simultaneous with in situ replacive gypsum crystallization. Accompanying displacive growth leads to volume increase in the poorly confined environment of the weathering zone that is susceptible to upward expansion.