The Great Salt Plains in Alfalfa County, in northwestern Oklahoma, the United States, is the only place in the world where hourglass-shaped selenite crystals are found. Millions of years ago this area was covered by a large inland sea. The sear was eventually cut off and the water evaporated away, leaving behind thick layers of salt that were subsequently covered by dirt and erosion from surrounding mountain ranges. As groundwater rises to the surface through the salt-saturated sand, it takes salt along with it and deposits them on the surface as a thin crust. It is the concentrated saline solution combining with gypsum that promotes the growth of selenite, a crystalline form of gypsum. These crystals are found buried only a few feet below the surface, under an area that’s 11,000 square miles in size.
Selenite crystals dug up from the lake bed. Photo credit: Neal/Flickr
Gypsum crystals are affected by the environment they grow in. The finer the soil, the more clear the crystals. The crystals found on the Great Salt Plains are chocolate brown in color due to the presence of iron oxide in the soil, and because these crystals form in wet soil, sand and clay particles are included within the crystal. These particles often form an "hourglass" shape inside the crystal. This hourglass shape is unique to selenite crystals that grow on the Salt Plains of northwest Oklahoma.
Aside from hourglass-shaped crystals, single crystal blades, penetration twins, and clusters are also found here. Some crystals that have been found here measured up to seven inches long, and complex combinations weighed as much as 38 pounds. Because these crystals are so unique, they were designated as the State Crystal of Oklahoma in 2005.
The Great Salt Plains itself is a protected State Park. However, every year between April and October, the west edge of the Great Salt lake is opened up digging, attracting rock enthusiasts from all over America and beyond. Collectors are permitted to take up to 10 pounds of crystals, but for personal use only. Selling of crystals is illegal.
A gypsum crystal showing the "hourglass" shape. Photo credit: www.mindat.org
Photo credit: Nate/Flickr
Photo credit: Justin Waits/Flickr
Photo credit: Nate/Flickr
Photo credit: www.okladot.state.ok.us
Photo credit: Neal/Flickr
Source: www.fws.gov
Love Digging? Check out these:
There is a slight problem with the following phrase: "Some crystals that have been found here measured up to seven inches and weighed as much as 38 pounds". One might think that a single 7-inch crystal weighed 38 pounds. That is impossible. The proper interpretation, as stated on fws.gov, is: "Exceptional individual crystals measuring up to seven inches long have been found, along with complex combinations weighing as much as 38 pounds". Thank you!
ReplyDelete