Cave of the Crystals
Cave of the Crystals or Giant Crystal Cave () is a cave connected to the Naica Mine at a depth of , in Naica, Chihuahua, Mexico. It takes the form of a chamber within the limestone host rock of the mine, and is about long with a volume of . The chamber contains giant selenite crystals (gypsum, CaSO), some of the largest natural crystals ever found. The largest is , with a volume of about , and an estimated mass of 12 tonnes. When it was accessible, the cave was extremely hot, with air temperatures reaching up to with 90 to  99 percent humidity. The cave is relatively unexplored because of these factors. Without proper protection, people can only endure approximately ten minutes of exposure at a time. The cave was discovered in April 2000 by brothers Juan and Pedro Sanchez while drilling in the mine. , the mine had reflooded and the cavern filled once more with the water rich in minerals required for the crystals to grow. A group of scientists in the Naica Project have been studying these caverns. Formation of the crystals. Naica lies on a fault above an underground magma chamber which is approximately below the cave . The magma heated the ground water which was saturated with sulfide ions (S). Cool oxygenated surface water contacted the mineral-saturated heated water, but the two did not mix because of the difference in their densities. The oxygen slowly diffused into the heated water and oxidized the sulfides (S) into sulfates () that precipitated as anhydrite (CaSO). When the overall temperature of the cave started to drop below , the hydrothermal and sedimentary anhydrite crystals dissolved, and gypsum (CaSO) crystals formed. The hydrated sulfate gypsum crystallized at an extremely slow rate over the course of at least 500,000 years, forming the enormous  crystals found today. Discovery. In 1910, miners discovered a cavern beneath the Naica Mine workings, the Cave of Swords (). It is located at a depth of , above the Cave of the Crystals, and contains spectacular, smaller ( long) crystals. It is speculated that at this level, transition temperatures may have fallen much more rapidly, leading to an end in the growth of the crystals. Giant Crystal Cave was discovered in April 2000 by miners excavating a new tunnel for the Industrias Peñoles mining company located in Naica, Mexico, while drilling through the Naica fault, which they were concerned would flood the  mine. The mining complex in Naica contains substantial deposits of silver, zinc and lead. The Cave of Crystals is a horseshoe-shaped cavity in limestone. Its floor is covered with perfectly faceted crystalline blocks. Huge crystal beams jut out from both the blocks and the floor. The crystals deteriorate in air, so the Naica Project attempted to visually document the crystals before they deteriorated further. Two other smaller caverns were also discovered in 2000, Queen’s Eye Cave and Candles Cave, and another chamber was found in a drilling project in 2009. The new cave, named Ice Palace, is deep  and is not flooded, but its crystal formations are much smaller, with small "cauliflower" formations and fine, threadlike crystals. Exploration and scientific studies. A scientific team coordinated by Paolo Forti, specialist of cave minerals and crystallographer at the University of Bologna (Italy), explored the cave in detail in 2006. To survive and to be able to work in the extreme temperature and humid conditions which prevent prolonged incursion in the crystal chamber, they developed their own refrigerated suits and cold breathing systems (respectively dubbed Tolomea suit and Sinusit respirator). Special caving overalls were fitted with a mattress of refrigerating tubes  placed all over the body and connected to a backpack weighing about containing a reservoir filled with cold water and ice. The cooling provided by melting ice was sufficient to provide about half an hour of autonomy. Besides mineralogical and crystallographic studies, biogeochemical and microbial characterization of the gypsum giant crystals were performed. Stein-Erik Lauritzen (University of Bergen, Norway) performed uranium-thorium dating to determine the maximum age of the giant crystals, about 500,000 years. A team led by A. E. S. Van Driessche directly measured the growth rates of these giant gypsum crystals using present-day water of  the Naica. They obtained a growth rate of , which is the slowest directly measured normal growth rate for any crystal growth process. Taking into account this rate, the largest crystals would have taken approximately 1 million years to reach their current size. Penelope Boston (New Mexico Institute of Mining and Technology), speleologist and geomicrobiologist specialist of extremophile organisms, realized sterile sampling of gypsum drillcores by making small boreholes inside large crystals under aseptic conditions. The aim was to detect the possible presence of ancient bacteria encapsulated inside fluid and solid inclusions present in the calcium sulfate matrix from its formation . Solid inclusions mainly consist of magnesium and iron oxy-hydroxide, but no organic matter could be found associated with the solid hydroxides. No DNA from ancient bacteria could be extracted from the solid inclusions and amplified by PCR. Microbial studies on fluid inclusions are foreseen to attempt to evidence the presence of ancient micro-organisms in the original fluid solution in which the crystals developed. At the 2017 meeting of the American Association for the Advancement of Science, researchers, including Dr. Boston, announced the discovery of bacteria found in inclusions embedded in some of the crystals. Using sterile methods, the  researchers were able to extract and reanimate these organisms, which are not closely related to anything in the known genetic databases. Other researches covered the fields of palynology (pollen study), geochemistry, hydrogeology and the physical conditions prevailing in the Cave of Crystals. Closure. The cave was featured on the Discovery Channel program "Naica: Beyond The Crystal Cave" in February 2011. Earlier, it was featured on the History Channel program "Life After People", in the episode "Depths of Destruction" of the second season. Additionally, these caves were also featured on the program "Angry Planet", in episode 311. Exploration has given credence  to the existence of further chambers, but further exploration would have required significant removal of the crystals. As the cave's accessibility is dependent on the mine's water pumps, once mining operations ceased, the caves were allowed to re-flood in October 2015. If the mining company decides to open another entrance, researchers might again enter to continue their work, according to a February 2019 report.