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Cabo Ortegal is one of the major ultramafic complexes outcropping in Iberia. Most rocks are variably serpentinized, and the characteristics of the process can be traced through the composition of the rocks. The major and trace elements change in the different units of the complex. Together with the wide range of oxygen isotope values (d 18 O from 3.9 up to 6.6‰), these changes lead to the conclusion that several stages of serpentinization took place at Cabo Ortegal. Each stage is characterized by the composition of the fluid that produced the serpentinization. Seawater does not have to be the main fluid in the process; an ultimate stage of serpentinization can mask the characteristics of a previous one.

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 metamorphic product 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, serpenfinites 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 chemical behaviour of carbonates and serpentine minerals can result in significantly different behaviour of commercial building stones. Thus, carbonates are resistant to weathering but suffer from acidic 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 mineralogy and geochemistry (including major, trace and volatile elements together with oxygen isotopes), in conjunction with their physical properties, would enable architects to select the appropriate interior or exterior use of these handsome building stones.

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Abstract:Presented herein is a cartographic procedure that is easy to utilise and at low-cost, which facilitates the first stages of planning and management of a naturally protected space and considers the geotechnical parameters that influence human activity. This procedure uses geographical information systems technology by combining the cartographies for the most influential parameters on the stability of the area (lithology, hydrogeology, geomorphology, slopes, lineament/fractures and seismicity) with geomechanical mapping generated from geotechnical parameters obtained through field and laboratory tests. This geotechnical mapping facilitates the division of a territory into zones according to each type of problem and generates a cartography for natural hazards. Using this information, it is possible to produce a cartography of constructive conditions or geotechnical hazards. This methodology has been validated by application to two natural protected spaces, "Las Batuecas-Sierra de Francia" and "Quilamas". The validation confirmed that the cartography procedure described herein is a preventive, and not a structural measure. It is a tool that delimits areas with different constructive use recommendations and limitations, and therefore, is useful for natural space managers.

Serpentinites are characterized by highly variable mineralogical, physical, and mechanical properties. Serpentinites from Moeche (North Western Spain) have been studied to establish their mineralogical, petrographic, and textural characteristics, as well as their physical and mechanical parameters and the factors influencing rock failure, to evaluate the possible use of these rocks either for new construction or for conservation-restoration of the architectonic heritage of the region. In this paper, we highlight the importance of a detailed mineralogical and petrographic characterization in the fracture zones, which will determine the viability of quarrying the stone. A strong correlation between the petrographic features and the uniaxial compression strength values has been observed. The most important aspects were found to be the rock texture, the mineralogical composition of the fracture area and foliation, although mineralogy was also found to be involved (% of carbonates) in the strength of the stone. An important preliminary result of the study was the low asbestos content of these serpentinites, which will help in the potential re-opening of the quarries.

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