GeoPic of the Week: Dolomite (pink) and Sphalerite (brown) In Dolostone

Dolomite and Sphalerite in DolostoneDolomite and Sphalerite in Dolostone

Dolomite (pink) and Sphalerite (brown) In Dolostone

Dolomite and sphalerite are two minerals present in limestone and dolostone in the lead and zinc districts of north Arkansas.  Dolomite commonly occurs with the sphalerite, however it is not an ore mineral and is considered worthless.  Sphalerite is the primary ore of zinc.  Zinc was mined in the lower end of the Buffalo National River in the late 1800s and early 1900s.  One of the largest mining communities was located at Rush, Arkansas.  Zinc is used as a coating of iron or steel to protect it from corrosion.  It is also used in batteries, small non-structural castings, and alloys, such as brass.  This mineralization is present in the Everton Formation.  It is thought that migration of warm mineral-rich fluids expelled by the pressure of the mountain building event that caused the Ouachita Mountains is responsible for the mineralization in northern Arkansas.  Note the brecciated texture (angular fragments) of the rock.  Open spaces, called cavities, in the rock caused the overlying rock to collapse, and break into angular pieces.  Mineralized water then flowed around the broken pieces and the dolomite and sphalerite precipitated in the open spaces.

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