The NSS Bulletin - ISSN 1090-6924
Volume 47 Number 1: 17-27 - October 1985

A publication of the National Speleological Society

Mineralogy of Rohrer's Cave, Lancaster County, Pennsylvania
William B. White, Barry E. Scheetz, Scott D. Atkinson, Dale Ibberson, and Catherine A. Chess


Rohrer's Cave, developed along the contact between the Cambrian Vintage Dolomite and the Kinzer shaley limestone, was opened by a sinkhole collapse in 1979. The cave's 275 meters of passage are floored in places with a brown mud overlying an intricately layered sequence of white, yellow, and gray sediment. In place of the usual calcite speleothems, the cave contains a bizarre collection of white and black soft mushy coatings and hanging forms resembling pinecones. It also contains brown stalactites and stalagmites of hydrated iron oxides. A boxwork-like form occurs as do patches of blue flowstone. The iron oxide speleothems are relatively pure but noncrystalline at the scale of X-ray diffraction. There is no evidence for other heavy metals with the iron. The black coatings consist of manganese oxides with exceptional concentrations (about 20 weight percent) of the heavy metals nickel, cobalt, copper, and zinc in various but approximately equal proportions. The white opaline or moonmilk-like deposits consist in part of noncrystalline hydrated aluminum silicates and aluminum phosphates. Their chemical composition and microstructrure identify them as the clay mineral allophane. The blue flowstone found in a few patches in the cave is also allophane containing a few percent of copper. The layered sediments consist mainly of allophane with small amounts of iron and manganese oxide forming pigmenting layers. All deposits contain large proportions of unbound water which is lost on drying to form loose fine-grained powders or thin flakes.

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