GypsumThe giant gypsum crystals in Mexico's "Cueva de los Cristales" are a stunning natural wonder featuring crystals up to 11 metres long.

These giant gypsum (hydrated calcium sulphate) crystals in the “Cave of Crystals” in the Naica mine, Chihuahua, Mexico pose an interesting problem: how are they formed. A Spanish-Mexican team led by Prof García-Ruiz et al. propose that these crystals are derived from "a self-feeding mechanism driven by a solution-mediated, anhydrite-gypsum phase transition". The solution from which the crystals grew were maintained in a very narrow, stable temperature range. It seems likely that related features will be discovered in the future.1

See Geology: April, 2007, v. 35, no. 4, where the crystals are featured on the cover.

• 1. Formation of natural gypsum megacrystals in Naica, Mexico,
  García-Ruiz, Juan Manuel, Villasuso Roberto, Ayora Carlos, Canals Angels, and Otálora Fermín
  , Geology, 2007, Volume 35, Issue 4, p.327, (2007)