HOURGLASS SELENITE CRYSTAL IN GLASS DISPLAY BOX - Oklahoma, USA

'HOURGLASS' SELENITE CRYSTAL
  
Great Salt Plains, Jet, Oklahoma, USA

Great Salt Plains Wildlife Refuge in Oklahoma is the only place in the world where selenite crystals with ‘hourglass’ inclusions are found. The crystals, which are a variety of gypsum, form just below the surface of the salt flats.

The reason for this hourglass pattern is not clear, but it may be that the bond between the molecules forming different faces varies, so that minute inclusions of lake sediment are incorporated into the crystal only when one set of opposite faces are growing.

Collecting at the site is now restricted. This crystal is from an old collection. It is presented in a gemstone box with a glass lid.
 
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