Herringbone Calcite

(Research on Egyptian herringbone calcite was funded by NSF Geology and Paleontology for 1999-2002.)

Herringbone calcite is a distinctively textured calcite cement that may hold clues to the chemistry of the water from which it precipitated (see Oxygen and Carbonate Precipitation, Herringbone Calcite, and Archean Carbonate Precipitation and Oxygen). The figure to the right shows a polished, etched slab of a thick layer of Archean herringbone calcite. It is characterized by serrate bands that are approximately perpendicular to its growth direction (up in the photograph). The bands are caused by progressive changes in crystal orientation which causes light to reflect differently. The scale at the top is in mm. (More herringbone calcite figures)

Herringbone calcite from caves and fractures in Eocene Egyptian carbonates has similar crystallographic characteristics. This herringbone calcite was used as sculpture stone by ancient (and modern) Egyptian, Roman, and Greek artisans. It is much better preserved than any other samples found so far (thin section photos, a 96k PDF file). Geochemical analyses do not conform to the predicted anoxic conditions (see 2000 GSA abstract by Tourre and Sumner). The calcite does not contain Fe2+ even though hematite (oxidized iron) was present in the environment. Very high concentrations of strontium are present, however. Continuing work will use geochemical analyses and TEM imaging to try to understand the origin of crystal defects and the cause(s) of the herringbone calcite crystal structure.



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Dawn Y. Sumner
Department of Geology
University of California
Davis, CA 95616
dysumner@ucdavis.edu