Giant Crystal Cave - National Geographic Channel now...

SECRETS OF THE CRYSTAL CAVE
Hidden deep beneath the surface of the Earth is one of the greatest natural marvels on the planet: a giant crystal cave with crystals up to 36 feet long and weighing 55 tons. But this scorching cavern could kill humans after just 15 minutes of exposure.
-The giant crystals found in the caves at Naica are softer than a human fingernail.
-The largest crystal found at Naica is 500,000 years old.
-The stunning crystal pillars are made from the same common mineral as drywall – it's called gypsum.
-The Naica cave's deadly heat comes from the depths of the Earth. Naica sits on a set of fault lines. A magma chamber a mile and a half down warms the water that flows throughout the mountain.
-The Naica principle cave "Cueva de Los Cristales" is 45°C and 100% humidity.
-The Naica facility pumps 16,000 gallons of water per minute out of the mine and runs 24-7.
-The water pumped from the Naica mine formed a lake in the arid Chihuahua desert and is also used to irrigate a golf course.
-Naica is one of the most productive lead mines in the world, and a huge supplier of the world's silver as well.
-The Naica cave actuality footage was shot on solid-state memory HD video cameras (tape-less) wrapped in plastic bags and pre-heated for three hours prior to entering the cave.
-The Naica Project team created a stop-motion robot and fitted it with a Nikon digital still camera powered by a custom software to capture beauty-shot sequences of the cave with 10-megapixel resolution.
http://channel.nationalgeographic.com/episode/giant-crystal-cave-3569/Overview#tab-facts