It’s been a hot minute since I’ve written about an oddball geological feature. This is largely because it was only supposed to be a 5 part series. However, through my research I discovered there is a plethora of strange geological formations that exist— not only on Earth, but in our solar system as well. Therefore, from now on I will title these posts as a volume, rather than a part. When the collection will end can only be determined by a lack of oddball geological features. Challenge accepted!
The other evening while watching one of my all-time favorite television series, which is Star Trek: Next Generation, something peaked my interest. In the particular episode I was viewing, the federation space ship Enterprise was stuck in orbit due to some sort of electrical interference coming from the planet below. In order to find the root cause of their problem, Captain Jean Luc Picard sent an away team down to the planets surface that consisted of Commander William Riker and Chief Operations Officer Data. Once they were transported, Data discovered what appears to be massive quartz crystals. The star of the episode was actually the Ferengi, but the crystals are what caught my attention.
In all honesty, the scene looked rather goofy, but it made me curious as to whether or not such mammoth crystals were capable of forming here on Earth. Lo and behold, I found a similar example that exists in a cave located in the Chihuahua state of Mexico.
Lying 300 meters (980 feet) below the surface of Naica, Mexico, the Cave of Crystals houses the world’s largest selenite crystals (gypsum, CaSO4·2 H2O) ever found on Earth. To date, the largest of these crystals found is 12 meters in length, 4 meters in diameter and weighs a mind boggling 55 tons. The cave itself was discovered in April 2000 by miners who were excavating a new tunnel for the Industrias Peñoles mining company, while drilling through the ancient Naica Fault. This region is predominantly mined for the silver, zinc and lead deposits that exist there. Upon discovering the cavern, it was deemed impassable due to it being flooded. It was eventually drained, however another challenge propagated for the miners and scientists curious over its existence.
In order for the scientists to properly explore the cave, they had to develop special refrigerated suits and cold breathing systems. This was due to the cave being extremely hot, with temperatures reaching up to 58 °C (136 °F). Another issue was that the cave also had a humidity of 90 to 99 percent. The reason for this extreme climate is because the cavern lies 2-3 miles (3-5 km) above an underground magma chamber, which heats the groundwater in the area. These extremes also played a major role in the actual development of the crystals themselves. It should be noted, the only reason this cave remained explorable is because the mining company continued to drain it. Without it being drained, it would eventually flood again.
Another interesting thing I learned, is that due it being drained, the crystals began to deteriorate when they came in contact with air. This is largely because gypsum is a soft sulfate mineral which is commonly associated with rock salt and sulfur deposits. Today, mining of this region has ceased, allowing the cavern to flood again. This also means that exploration of the cavern has ceased as well.
How did these crystals form?
Due to the close proximity the cavern has to the magma chamber below it and the fact it’s made of limestone, plays a major role in the development of these mammoth crystals. Typically, gypsum forms in lagoons where ocean waters high in sulfate and calcium content can slowly evaporate and be regularly replenished with new sources of water. Limestone has a high level of calcium content in it. In the case of the gypsum in the Cave of Crystals, the magma heats the groundwater that is saturated with sulfide ions (S2−). Cooler oxygenated surface water eventually comes in contact with the heated saturated water, but due to the difference in densities, the two do not mix. Overtime, the oxygen from the cooler water begins to slowly diffuse into the heated water and oxidizes the sulfides (S2−) into sulfates (SO42−). This causes crystallization to occur in the form of gypsum. The gypsum in these caverns crystallized over eons (500,000 years), allowing the enormous crystals we know of today to form.
I’d also like to point out that this region was mined for over a hundred years. During that time span, multiple caves with intricate crystal systems were discovered— the first of them being the Cave of Swords, which was uncovered in 1910. In total, 5 caves were discovered: Cave of Crystals, Queen’s Eye, Candles Cave, Ice Palace and Cave of Swords. It would appear the only one with massive crystals is the Cave of Crystals, while the others consisted of much smaller ones in comparison. I don’t know about you, but those all sound like mini temples from the video game Legend of Zelda to me.
On a personal note, the coolest aspect of finding out about these crystals, with regard to the Star Trek episode I viewed, is that at the time of episodes production, crystals of that size did not exist— they were entirely fictional. From a historical point of view, science fiction was predominantly based off of speculation and imagination e.g. Journey to the Center of the Earth. Interestingly enough, this is especially true when it comes to geology as well.
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Bibliography:
https://en.wikipedia.org/wiki/Selenite
https://en.wikipedia.org/wiki/Cave_of_the_Crystals
https://en.wikipedia.org/wiki/Gypsum
https://mineralseducationcoalition.org/minerals-database/gypsum/
