In 2000, one of the most unusual and splendid caves was found in Mexico by miners. Located only a mile from an upthrust of magma, this cave is 112 degrees Farenheit and at 90-100% humidity, limiting greatly the amount of time explorers can spend in it. It is a spectacular cave, with gigantic crystal formations thought to be 600,000 years old.
The crystals formed underwater; as water saturated with calcium sulfate heated in the cavern selenite molecules crystallized and grew, undisturbed, to giant proportions. The cave was drained (by unknowing miners) in the 1980's and stopped the process of growth. Who knows what we may find further on, in the heat and water?
"It is unquestionably magical that the cool white rays of moonlight can originate deep underground in a black chamber that is, at least in my perception, white hot." (Richard Fisher, photographer, comments on the huge selenite crystals.)
Geodes are normally formed by volcanic or sedimentary geologic activity - a cavity in the rock is formed, inside which crystals begin to grow, such as amethyst, quartz or a number of others. Most geodes are small enough to fit in your hand, but this one is large enough to climb inside. The crystals found here are gypsum.