• Specimen Number

  22

• Description

  White unshaped block of quartz with feldspar (?) showing no indication of fused grains characteristic of quartzite. The layered look, absent pervasive fractures, may be due to perthitic intergrowths (as with graphic granite) during pegmatite crystallization, or possibly alteration during shearing.

• Classification

  Hydrothermal. Pegmatite. Vein.

• Location & Occurrence

  Our contact  from the Mississippi State Survey  stated that this specimen is not likely to have come from Mississippi.  We reached that conclusion independently and earlier.  Though it's remotely possibe that it's a fragment of a larger boulder/cobble from river gravel carried southward from the bedrock craton to the north during Mississippi River transport, as with Lake Superior Agates found in Cenozoic gravel deposits, this interpretation is implausible owing to the angularity and large size of the specimen.  This angularity requires that none of the exterior rounded cortex survived, which, in turn suggests a large boulder.

• Geological Age

  Unknown.

• Geoheritage

  Likely an error in collecting/constructing. This highlights the importance of having a good record of collection and subsequent handling, a problem for all collections.  The only alternative ist hat it's Mississippi River transport from ancient terrains to north. Link below indicates that Lake Superior Agates and Sioux Quartzite are indeed found in the state.  However, all exotics have rounded cortex and appear smaller than the angular specimen on the Rock Wall.  Conversely, in gross shape and lithology (see closeups), this specimen resembles #39, a pegmatite from South Dakota, suggesting that it's also from there.

• Links

  Link to State Geological Map from USGS.  Link to Office of Geology. Link to craton-derived samples from Mississippi report Mississippi's Gravel Deposits.

• Other

  This specimen raises the specter of sloppy record-keeping or handling. Worse, it suggests a deliberate, wanton substitute of one stone for another during construction.

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