986K views · 16K reactions | In the year 2000," the Cave of the Crystals” was discovered by miners excavating a tunnel for the Naica Mine in Mexico. The main chamber contains some of the largest natural crystals ever found in any underground cave. The main chamber contains giant selenite crystals (gypsum, CaSO4·2 H2O), the largest natural crystals ever found. Commentary by: ROBERT SEPEHR Amazing Geologist | Amazing Geologist | Facebook