Giant Crystal Secret Recipe Found

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April 5, 2007 — Mother Nature’s secret recipe for cooking up the staggeringly huge, pillar-like crystals of Mexico's newfound Cave of Crystals has been worked out by mineral researchers.

It turns out that with just the right pinch of minerals added at the right times for a few million years to a warm subterranean broth, you too can grow gypsum crystals 35 feet long and as thick as tree trunks. Gypsum, incidentally, is the same stuff that’s ground up to make plaster of Paris.

A team of researchers from Mexico and Spain have hit on the factors that created the otherworldly crystal "beams" that were discovered by miners in 2000 in a cave of the Naica Mine in northern state of Chihuahua. By studying the crystals in the cave and testing some fluid mixtures in a laboratory, it appears that the crystals formed in delicately balanced mineral water that stayed within a narrow range of temperatures for a very long time.

"Actually the cave was filled with water until few years ago when continuous pumping requiring for mining has lowered the underground water below 290 meters deep (950 feet), the depth at which the cave is located," explained mineralogist Juan Manuel García-Ruiz of the Laboratory of Crystallographic Studies in Granada, Spain. He’s also the lead author on a paper explaining the mega crystals in the April issue of the journal Geology.

Like the air now in the cave, the water in which the crystals formed was at least 126 degrees Fahrenheit (52 degrees Centigrade) and was enriched with the compound calcium sulfate from about 23 million years worth of geothermally heated water percolating upwards. 

The enriched water dissolved sulfur-bearing rocks along the way and deposited that as hot anhydrite – which is essentially just another form of gypsum, except with no water trapped inside the molecules.

"The key point is that anhydrite is stable above 58 degrees Celsius (136 degrees F), while below that temperature gypsum is the stable form," said García-Ruiz. "Therefore until the temperature was kept above 58  degrees C anhydrite was stable."

Below that temperature, the anhydrite dissolves and the gypsum crystals started to form. That that’s not the entire recipe for giant crystals, he said.

"To grow very large crystals it is required to form only very few nuclei (‘seed’ crystals) and to feed them continuously with very small amount of calcium sulfate for extremely long times," said García-Ruiz, "something that is provided by the small but continuous dissolution of anhydrite in the mine."

So the trick is having just enough — but not too much — calcium sulfate in warm water that’s cooling — but not cooling too fast.

"For these huge crystals to form, it is mandatory that the cave environment never cool below 45 degrees (113 degrees F), according to our calculation," García-Ruiz told Discovery News.

"Wow! These are essentially single crystals," remarked cave geologist Laurence Davis of the University of New Haven, in Connecticut. He had not heard of the giant crystals until reading the Geology paper.

As for the science behind García-Ruiz’s recipe, "This is pretty standard cave stuff," Davis said. "It sounds pretty good to me."