Features and Origin of Red Clays in Castafiar Cave: A Touch of Colour

Abstract

In Castaiiar Cave (Caceres, Spain), coatings of red clays cover the walls of the chambers, coexisting with diverse speleothems of aragonite, calcite, huntite and dolomite. The mineralogy of the clays is mainly illite, chlorite, kaolinite, smectite, quartz and Fe oxides and hydroxides such as goethite. They can be transported into the cave by infiltration waters or form by in situ alteration of the host rock: layers of dolomite rich in Fe and magnesite interbedded with greywackes and shales. Present-day hydrological conditions in the cave and conditions during the formation of speleothems have determined that the clays have not been transported by any flooding or seepage, but mostly staying in situ, and not included into carbonate crystal forms . Thus, most of the well-preserved speleothems are white and not stained, conforming an interesting chromatic contrast with the red clays that represent an additional attraction in this show cave.