Halite xx (rock salt, common salt) [NaCl] on wood

Groundwater seeps into artificial cavities created by mining through pores and cracks in the rock. On its way through the rock layers, it dissolves salts and minerals. In this case, saline mine water wetted the end of a support, then evaporated in the warm air underground, leaving a bizarre crown of cube-shaped rock salt crystals on the wood over time.