Giant underground crystals

[science_spot]

Mexico's Cueva de los Cristales (Cave of the Crystals) is home to the largest known natural crystal formation in the world.  Crystals of gypsum up to 36 feet long cross through this beautiful cave, 950 feet below the Naica Mountains.

 

In 2000, when a nearby mining operation started pumping the water out of the 30 x 90 foot cave, exploration of the area began, and the crystals were discovered by two miners.  Scientists are advising the mining company to preserve the cave as it is the only known crystal structure of this size found on Earth!  Now the temperature in the cave is a steady 120 degrees, with 80% humidity due to a special door constructed to seal it from the rest of the mine.  The cave is dry now because the mining company continues to pump over 13,000 gallons of water out of that area every minute.  If they ever stop, the cave will fill with water and the crystals will start growing again.

How did the crystals get there?  Scientists knew the cave was full of mineral-rich water.  Further studies showed the mineral gypsum anhydrite formed these long crystals because of the very steady temperature conditions around 135 degrees.  In order to maintain there current crystalline form, the temperature must hold near a steady 120 degrees with high humidity (about 80%).  They believe volcanic activity millions of years ago that formed the mountain range here also deposited the gypsum anhydrate which later dissolved in high temperature water.  The details were published in the journal Geology. 

 

 

National Geographic provides this video below of the cave (as well as the above pictures in this post).  It's pretty dark (it's a cave), but you can see the crystals occasionally.

 

So how do crystals form, in general?  When there is a solvent (such as water), saturated with salts, some of the salt in solution can become stable as a solid.  Usually when this happens (on a very small scale), the salts are re-solubilized.  This can ocur many times, but sometimes, the solid salts are very stable and more salts come out of the solution and add to the solid mass.  This solid mass forms a very regular pattern - the crystal.  Certains conditions such as decreasing temperature and increasing pressure can encourage crystal formation, but this isn't a requirement.  The slower this crystal formation process, the larger the crystal will grow (assuming there is alot of salt available).

You can easily grow crystals at home.  Check out juliehood's stalactites/stalagmites experiment, or try the super-easy classic version:  Dissolve as much salt into very warm water as you can.  Pour this solution into a tall glass.  Hang a piece of string or yarn down into the water - it's easy to weigh it down with a paperclip tied to one end, and hanging from a pencil laid across the top of the glass (see picture below from NASA).  As the water cools, crystals will form (give it up to week).  See if you get different crystals if you use different salts, such as sea salt, kosher salt, table salt and epsom salts.

 

 

Tonya

AKA sunmoonstars

The Science Spot

 

[used2chaos]

Jun. 13, 2009 at 1:45 PM

We saw this show on Natgeo - so cool!

[Nanette77318]

Jun. 13, 2009 at 2:29 PM

Fascinating! Crazy amazing!

[MythicMMM]

Jun. 13, 2009 at 3:01 PM

Holy cow!!!

[clairandamjones]

Jun. 13, 2009 at 3:29 PM

That is super cool!  I once had the opportunity to go caving, for real, with the lamp-helmet and all.  It was an amazing experience.  Thanks for sharing this with us!

[You_Are_Invited]

Jun. 13, 2009 at 4:50 PM

Thanks Tonya! This will be our first experiment of the summer!

[t1gger143]

Jun. 13, 2009 at 8:46 PM I saw this on tv. I thought it was very interesting and the precaustions that they have to take due to the heat Wow!

[aluvk4evr]

Jun. 14, 2009 at 1:10 PM

Wow, that's amazing. They're huge.