This is the Cueva de Cristales found in the Naica Mine, Chihuahua, Mexico.
These are Selenite crystals (gypsum) and are the largest crystals ever discovered.They are 1000 feet down in a limestone host rock where they are mining for lead, zinc and silver. The miners had to drill through the Naica fault, which they were worried would flood the mine, and this is what they discovered.
From a geologist colleague who visited this place.... Amazing. His commentary:I got the chance to see that this past year. We wrangled a tour of the Naica mine from Penoles and got into the Cueva de Cristales. That had to rank as one of the most spectacular things that I've ever seen in my life. You know, I like to think tha t I'm pretty handy with a camera, but to get those shots ... those guys were working hard. They keep the room completely sealed. The temperature inside is 140-150 degrees. Humidity is 100%. That means that when you come in from the ambient mine temperature everything that is glass fogs over. Glasses, camera lenses. After 4 or 5 minutes your clothes are soaked. After about 10 minutes you have to leave before you go down with heat stroke. Seriously.
There have been a couple of teams of photographers (Smithsonian, Nat'l Geo) to visit the mine, solely to photograph the Cueva de Cristales, and the other, the Cave of Swords (still huge, but smaller crystals). They brought water-cooled suits so they could stay inside longer, and low-temp ovens so they could heat their gear prior to entering to prevent the condensation. Pretty tough conditions ... but they got some cool photos that the tourist could never get. Those things are for real. In a couple of the shots the photographer used a wide-angle lens and it gives the appearance that the room is bigger than it really is. If I remember right, it was probably about 40-50 feet across. Crystals bigger around than tree trunks. Certainly a tick-mark on the life's list of cool things to see!!