Gypsum

Another example of gypsum, this piece was collected from a mine in Mexico. Amazingly, the gypsum formed over a piece of rope and some metalwork. The mine had been abandoned for decades, and in the absence of human activity, geologic forces took over. Gypsum crystals grow faster than some other minerals, like Quarts. Quartz crystals this size would have taken hundreds, or even thousands of years to grow, depending on the conditions. In another part of Mexico, there is a cave with gypsum crystals 30 feet long, and several feet across.