| HALITE
 
 
 
Halite
is an evaporative sedimentary rock composed primarily of the mineral 
halite 
(sodium chloride). Halite beds form when seas and playas dry, precipitating 
their mineral content. Some halite beds are more than 1000 feet thick. 
 Some of the more interesting 
halite beds reveal the history of the 
Mediterranean basin, as some of these salt beds lie beneath the sea, and must 
have formed when the Strait of Gibraltar closed and the Mediterranean Sea dried 
out. This event (or series of events) is called the Messinian Salinity Crisis 
and occurred nearly 6 million years ago. Evidence exists that the dry basin may 
have been 3 to 5 kilometers below sea level (far deeper than any current dry 
land), enough to experience very high pressures (50% greater than sea level air 
pressure today), and consequent very high temperatures due to adiabatic heating: 
up to 80°C (176 °F) at the greatest depths.
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