Colour Palette

The colour of those cave mineral formations composed of the common carbonate minerals calcite and aragonite is usually restricted to shades of white and brown, depending on impurities such as clay minerals and organic matter. However, when certain metal ions (particularly copper, zinc, nickel, and iron) leach from ore deposits in the overburden and are incorporated in trace amounts, the speleothems can exhibit much more colourful hues, including pure reds, greens, or blues. There are also speleothems formed by intrinsically colourful minerals, such as baryte, celestine, and fluorite. In any case, such colourful speleothems are quite rare!