Really, that’s all I said for like 5 minutes after seeing this picture for the first time:

Those are PEOPLE, for scale. Here’s another pic, just to put you in a little more awe:

These are the largest crystals yet to be found on Earth, with some reaching over 30 feet in length! As reported in NG, The Cueva de los Cristales is located 1000 feet below ground in the Chihuahua desert, and was discovered in 2000 during drilling for a nearby lead and silver mine. The cave is excrutiatingly hot and humid – 112 degrees F and 90-100% humidity! The cave is so hot, that suiting up to go inside is sort of like doing a reverse space walk. Everyone has to wear ice packs, full body insulation, and a respirator mask in the cave.

The reason the cave is so hot is also part of the reason the crystals formed here. The cave lies above a magma resovoir, which heated the local groundwater. Until 1985, when the mining operation lowered the local water table to extend the mine, the cave was completely submerged in this super heated groundwater. As the magma cooled, the water in the cave cooled enough to deposit selenite, a form of gypsum. The environment in this cave was stable enough over hundreds of thousands of years that the selenite crystals were able to continue growing uninterrupted.

We know there are massive gypsum deposits on Mars (ref: my thesis!), and we know that Mars has been much more tectonically stable than the Earth, so who knows? We might find crystal deposits on Mars to dwarf Cueva de los Cristales. Everything’s bigger on Mars anyway, right?