Characterization of serpentinites to define their appropriate use as dimension stone

Abstract

Abstract: Many questions arise when considering the appropriate use of building stones such as serpentinites. The commercial names of these rocks, collectively grouped as Green marbles ,have no correspondence to their actual mineralogy, geochemistry and/or physical characteristics. Serpentinite being the hydrated product of an ultramafic parent rock and not a metamorphicproduct of limestone as implied by the term marble . However, the serpentinites most widely used for ornamental purposes come from India (e.g. Rajasthan Green, Emerald Green) and in these the original mineralogy has been almost completely converted into carbonates. By contrast,serpentinites from elsewhere (e.g. Vermont Verde Antique from the USA and Verde Pirineos from Spain) do preserve some of their original mineralogy. The different physical and chemicalbehaviour of carbonates and serpentine minerals can result in significantly different behaviour of commercial building stones. Thus, carbonates are resistant to weathering but suffer fromacidic cleaning agents in interior use; whereas serpentinites, with a high content of talc, used on external faces undergo an increase in volume and a consequent rapid degradation. Accurate and precise characterization of serpentinites, including information on their mineralogyand geochemistry (including major, trace and volatile elements together with oxygenisotopes), in conjunction with their physical properties, would enable architects to select the appropriate interior or exterior use of these handsome building stones.