Minerals and Crystals Part 2 of 2
Yesterday's post featured the Mohs scale. We, as jewelry making enthusiasts are mostly interested in the crystalline minerals at the top of the scale like quartz, rubies, diamonds. But near the bottom of the scale, at number 2, is gypsum, the stuff used for making drywall.

1000 feet underneath the Naica Mountain in Mexico's Chihuahuan Desert is a remarkable natural wonder, a cave full of rare translucent giant gypsum crystals. The cave is in a working silver, lead and zinc mine and was first discovered by miners.

Some of these gypsum crystals are as long as 36 feet or 11 meters making them the world's largest natural crystals.  If you look carefully at the picture above, there is a man on the left, dwarfed by the crystals. One geologist called the Cueva de los Cristales (Cave of Crystals), "the Sistine Chapel of crystals". The crystals slowly formed in mineral rich water over half a million years in the stable but extreme conditions in the cave (that's how many of our favorite gemstone minerals formed too). The temperature inside was unreal - as high as 136 degrees Fahrenheit (58 degrees Celsius) when the cave was completely filled with water.

The crystals are not growing at the moment as the mining company has pumped all the water out. The humidity though is still a drenching 80% or more. The cave temperature is still well above 110 degrees Fahrenheit and the crystals are hot to the touch.

This National Geographic video shows a team of scientists exploring the cave - a highly dangerous thing to do. The extreme heat and high humidity combination mean that the human body cannot cool down because sweat doesn't evaporate. So the explorers only spent 10 minutes looking around and even that was twice as long as the safe limit! When they came out, their pulse rates and blood pressures were dangerously high!

More dramatic pictures can be seen on the National Geographic site.

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