salt plains are a unique geological area; the 11,000-acre
barren area is near perfectly flat with a wafer thin salt
crust. It is classified as the "largest such saline flat
in the central lowlands of North America".
salt was formed by repeated flooding by sea water millions
of years ago. The sea water was cut off from the sea and
evaporated, depositing thick layers of salt. The area was
subsequently covered by erosion from mountain ranges.
the plains, ground water travels through the salt-saturated
sand and comes to the surface where it evaporates, leaving
the crust of salt. The concentrated
solution combines with gypsum to promote selenite crystal
growth in a portion of the salt flats.
is Selenite, and How are Selenite Crystals Formed?
is a crystallized form of gypsum. Chemically, it is a hydrous
calcium sulfate. Gypsum is a common mineral that takes on
a great variety of crystal forms and shapes. On the Salt Plains,
the crystals are formed just below the salt encrusted surface.
They are seldom found deeper than 2 feet below the surface.
Crystals take on the characteristics of their environment;
the finer the soil, the more clear the crystals. Iron oxide
in the soil gives the crystals their chocolate brown color.
What is So Special About These Crystals?
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 cannot be found in selenite crystals in
other places of the world; it is only found here at the
Salt Plains of NW Oklahoma.
this is the only place in the world to find these crystals,
the selenite crystal with the hourglass-shaped
inclusion was designated as the State Crystal of Oklahoma
on April 4, 2005. Learn
crystals, penetration twins, and clusters are the typical
crystal shapes most frequently encountered on the refuge.
Exceptional individual crystals measuring up to 7 inches
long have been found, along with complex combinations weighing
as much as 38 pounds.
places on the Salt Plains, gypsum and saline solutions in
the soil are sufficiently concentrated to promote crystal
temperature and brine conditions are ideal,
the crystals may form very rapidly.
heavy rains or floods bring great quantities of freshwater
to the plains, some of the selenite crystals may go back
into solution until conditions are right for recrystallization.
July 30, 2007
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