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First, mea culpa. Last week I said Jeffrey Bada was a student of Stanley Miller’s at the University of Chicago. However, a press release from NASA Goddard Space Flight Center in the November 11 Star-Ledger indicates that Bada was Miller’s student at the University of California San Diego, where Miller went after leaving Chicago. Coincidentally, I also saw Harold Holzer interviewed by Brian Lamb on last Sunday’s Q&A program on PBS. I cited Holzer’s article on Election Day 1860 in the Smithsonian magazine in the same column last week. I also finished that column with a note about my preference for writing about intelligent animals such as the late Alex, the famed African grey parrot. In Sunday’s Book Review section of the New York Times I found that Irene Pepperberg has written a book, "Alex and Me", about her 30 years with Alex. It should be very interesting.
After venting last week about the distressing situation involving a change in health plans for us Bell Labs, now Alcatel Lucent, retirees, I found an article in the November National Geographic that reminded me of more pleasant times at Bell Labs. For about half my time there, I was involved in one way or another with crystal growth. I’ve written about my work growing germanium and silicon single crystals and other semiconductor compounds such as gallium arsenide and gallium phosphide. I also dabbled a bit in garnets and tungstates and ill-fated attempts to grow diamonds. The crystals I grew ranged in size from very thin layers of gallium phosphide single crystal material for light-emitting diodes (LEDs) to crystals of silicon and germanium about the size of my thumb.
Other colleagues at Bell Labs were growing much larger crystals of quartz or ruby, some of which were a couple inches in diameter and up to a couple feet long. The rubies were not for jewelry but for laser work. By the time I retired from Bell Labs in 1989, the semiconductor industry had progressed to growing silicon single crystals a foot in diameter and several feet long. The National Geographic article by Neil Shea titled "Crystal Palace" tells about crystals in a cave in Mexico that dwarf the crystals of my experience. Some of the crystals range up to several feet in width and 37 feet in length! The finding of impressive crystals by miners in lead and silver mines in Mexico was not an unusual occurrence. However, in the year 2000 in a remote region of northern Mexico, miners in the Naica mine came upon a wondrous cave almost a thousand feet below the surface; the cave is now known as the Cueva de los Cristales, Cave of Crystals.
I remember mentioning these crystals earlier but now more is known about their origin and the conditions under which they were formed. I’ve been in a few caves in my life and, as I recall, they were relatively cool places. Not so the Cave of Crystals. The temperature in the cave is 112 degrees Fahrenheit. You might say, "That’s not so bad. I’ve been in Las Vegas when the temperature was 110." (I have been there when it was that hot and found it brutal!) OK, but how often have you heard or said , "It’s not the heat, it’s the humidity."? Well, the humidity in the cave is 90 -100 percent! Under such conditions, the danger of deadly heatstroke is real and spending more than 20 minutes or so there means risking your life.
Shea describes going into the cave wearing an vest containing packets of ice, another vest to protect the ice from the heat, an orange caver’s suit, a helmet and respirator mask through which ice-cooled air is blown, boots and gloves. Even all this gear doesn’t rule out the danger of a visit to the cave. Shea and his guides apparently stayed a half hour and he says he was drenched in sweat and his veins were throbbing as they left the cave.
So, what are the crystals and how did they form? A Norwegian geologist, Stein-Erik Lauritzen, has dated the largest crystals by analyzing for thorium and uranium and his preliminary results indicate the crystals to be about 600 thousand years old. An Italian group led by Anna Maria Mercuri have found 30,000-year-old pollen grains in the crystals. The presence of these grains suggest that the area was once forest, not the desert it is today. The crystals themselves are a mineral called selenite, which is a form of gypsum, a hydrated form of calcium sulfate containing two molecules of water.
The history of the crystals’ formation begins many millions of years ago when our Earth was rife with volcanic activity. The molten magma coming up near the surface of the Earth left behind a wealth of ores that provided not only the lead and silver for the miners but also minerals that would later form the crystals. About one or two million years ago things began to cool and caves were formed. Water in the caves began dissolving some of the minerals, including a form of calcium sulfate known as anhydrite.
About 600,000 years ago, the cave had cooled down to 136 degrees Fahrenheit. At this temperature, the hydrated calcium sulfate begins to precipitate out as crystals of selenite. The scenario proposed for the growth of these huge crystals is that in the Cave of Crystals the temperature remained at about 136 degrees, kept warm by the molten magma below the cave, for lo these 600 millennia. As water leaked down into the caves it dissolved the calcium sulfate and in the Cave of crystals the selenite kept precipitating out on the crystals, which over 600 millennia built up to lengths as high as a 3- to 4-story building.
All this crystal growth came to an end in about 1985, when miners were unaware that they had pumped the water out of the cave. Actually, they were unaware that there was a Cave of Crystals until its discovery in 2000. Today, there’s concern that, without the water that supported the crystals, they may bend and/or break under their own weight. Selenite is not a hard material and can be scratched by your fingernail. There’s also concern about looting and the possibility that blasting from the mining operations could damage the crystals. Even now, with the temperature down to 112 from 136 degrees, it hardly seems likely that the cave will become a tourist attraction. This is fortunate, insofar as preserving the crystals is concerned. The mining company is reportedly dedicated to preserving the site but, at the same time, they are in the mining, not the crystal business.
Finally, a note for any chemists out there. When I saw the word "selenite" I thought of selenium and the fact that I saw in one chemistry text that there are selenium compounds known as selenites. Strangely, although I didn’t try very hard, I didn’t find any particular formula for such a selenite. Gypsum, which is calcium sulfate with two molecules of water, comes in at least three forms - selenite (a transparent, cleavable crystalline form), alabaster (a fine grained white form) and satin spar (a silky fibrous material). Apparently, the word selenite in our gypsum case derive from the Greek for moon and hence "moon rock", which alludes to its opal-like appearance in certain forms. For those unfamiliar with gypsum, it’s got a lot of uses, two prime uses being in drywalls and plaster.
Well, so much for crystals. Now it’s back to trying to decide whether to ditch my doctors and keep the new medical plan foisted upon us by Alcatel Lucent (it’s free for me) or pony up five or six thousand dollars a year for another plan that let’s me keep my doctors (see last week’s column). Oh for what seem now like the carefree days when I worked with crystals!
Allen F. Bortrum