A rare glimpse into the cave of crystals

Mexico's Cave of Crystals stunned geologists when it was first discovered in 2000. The underground chamber contains some of the largest natural crystals ever found - some of the selenite structures have grown to more than 10m long. Professor Iain Stewart of the BBC got a rare glimpse of the subterranean spectacle.

Nothing really prepares you for the extremes of that cavern. It's about 50C in there, but it's the virtually 100% humidity added on top that makes it a potential killer. That combination means that when you breathe air into your body, the surface of your lungs is actually the coolest surface the air encounters. That means the fluid starts to condense inside your lungs - and that's really not good news. When the cave was first discovered it was just an accident. Miners working in the Naica silver mine broke through the walls of the cavern and were astounded to discover these enormous crystals - the biggest anywhere on Earth. But when the first people went in to explore, they were almost overcome by the conditions. So one has to wear a special suit to enter the cave and be very careful not to tear it on the crystals.           The cave is at risk of being closed Despite all the dangers, the sheer beauty of the place is overwhelming. It's such a glorious place, it's like being in a modern art exhibit.  Only a handful of geologists that have ever been in there, and so it was a privilege to be allowed to film it. Yet remarkably, for the people who own and run the Naica mine, the crystal cave is a side-show, a distraction. They don't make any money out of it and sooner or later, when the economics of the mine change, it will close. The pumps will be taken out, the mine and the cave will flood and the crystals will once more be out of our reach. But perhaps we should console ourselves with the thought that here are certainly lots more crystal caves waiting to be discovered. For starters, the geology of the area around the cave suggests that there could be more crystal caves around Naica. But more broadly, the Earth's crust must be riddled with wonders like this. We know more about the outer edges of the Solar System than we do about the first kilometre of the Earth's crust. As we learn more about the crust, we can be sure that there will be discoveries even more spectacular than Naica.