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 80C (176 F) at the greatest depths.

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