Gothic-Arch Calcite from Speleothems of the Bohemian Karst (Czech Republic): Its Occurrence, Microscopic Ultrastructure and Possible Mechanism of Growth

Gothic arch calcite, a specific crystallographic variety of calcite known from some hot springs and tufa streams, has been newly recognized in the Koněprusy Caves. The gothic-arch occurs on exteriors exotic coralloid speleothems where it coexists with scalenohedral (dogtooth) spar crystals. crystals exhibit microscopic ultrastructural features including deeply eroded topography, etch pits, spiky ribbon crystallites, pointing to its extensive natural etching. Many calcites originated as late-stage, secondary overgrowths older, etched dogtooth Its characteristic outward curvature resulted recrystallization etching-liberated fine carbonate grains formed needle-fiber laths, which were accumulated bound faces at bases corroded These intimately coexisting destructive constructive processes crystal corrosion growth probably mediated by bacteria, fungi, or other microorganisms. Fluid inclusions embedded point vadose setting temperatures below ~50 °C. This, combined wider geological context, indicates that gothic only during late Pleistocene Holocene epochs, when cave, initially hypogene fluids deeper subsurface, was uplifted subaerial exposed meteoric waters seeping topographic surface. radiocarbon analysis shows are generally older than ~55,000 years, but surface layers still reveal weak 14C activity, suggesting microbiologically alterations may have occurring locally until now.