Description
Here we have a beautiful cluster of well formed, bicoloured Gypsum with dark gray base and colourless-transparent terminations. The crystals here are sharp edged and highly lustrous with only minor edge wear. Prismatic crystals of Gypsum (Selenite) from "Rosignano" have an anthropogenic origin, i.e. they formed on the internal surfaces of the transportation pipes of salt brine from the halite deposits of Buriano (Montecatini Val di Cecina) and Saline di Volterra (Volterra) to the soda factory of Rosignano Solvay. During the transport process, the brine temperature decreases and gypsum precipitates from the supersaturated solution, forming crystals whose colour and habit vary according to the pipe material. A large number of Gypsum specimens was recovered at the beginning of the 1980s, when the company Solvay carried out the substitution of the pipeline of well salt brine, more than 30 km long, from the halite deposits to the factory of Rosignano Solvay (Marchi et al., 2005; Orlandi, 2006).