@piggo @piggo Right. Now I recognise it. It reminds me of caves in Germany south of Harz mountains near Nordhausen and Kyffhauser which is full of gyps (https://en.wikipedia.org/wiki/Barbarossa_Cave). very "different" experience (in comparison to karst caves): https://www.google.com/search?q=barbarossa+hoehle&tbm=isch&ved=2ahUKEwjjtKyG-Lr7AhX1y7sIHaTmBYIQ2-cCegQIABAA&oq=barbarossa+hoehle&gs_lcp=CgNpbWcQAzIHCAAQgAQQGFAAWMMDYJcFaAFwAHgAgAE9iAE9kgEBMZgBAKABAaoBC2d3cy13aXotaW1nwAEB&sclient=img&ei=7ih5Y-OFBvWX7_UPpM2XkAg&bih=894&biw=1612&hl=en

@FailForward the cool thing about this mineral is it's partly water soluble and in the right soil / clay, it regrows. So you can go to the same site after a month and there are new crystals freshly grown