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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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Podiform chromitites occurring in the ultramafic bodies of Calzadilla de los Barros, in the Ossa-Morena zone of the Iberian Massif (SW Iberian Peninsula), were deformed and metamorphosed together with their host rocks, leading to the development of variably complex patterns of zoning in chromite grains. These patterns consist of cores with variable composition surrounded by thin rims of porous chromite. Two types of zoned chromite are observed in chromitites: (1) crystals with zoned cores characterised by progressive Mg# [¼Mg/(Mg þ Fe 2þ )] decrease from inner to outer core, surrounded by Fe 2 O 3 -poor, porous rims, and (2) crystals showing the opposite chemical trend in cores (progressive Mg# increase from inner to outer core) and Fe 2 O 3 -rich porous rims. Mgrich chlorite is the only silicate mineral forming the matrix of all chromitites and filling most pores in chromite rims. Accessory chromites in dunites show complete transformation to ferrian chromite and Cr-rich magnetite. However, some of them exhibit complex chemical and textural zoning with three concentric zones (from inner to outer core and to inner rim) characterised by progressive Mg# increase and Cr# [¼Cr/(Cr þ Al)] decrease, surrounded by an outer rim with almost the same composition as the inner core. Some chromite grains from massive chromitites (defined here as higher than 85 vol.% chromite) still preserve inner core compositions unaffected by metamorphic transformation. These inner cores show high-Al composition (Cr# ¼ 0.48-0.52) with Mg# ranging from 0.65 to 0.70. These compositions resemble those reported for Al-rich, podiform chromitites in ophiolites elsewhere and indicate that chromitites from Calzadilla de los Barros derived from a MORB melt type in a MORB or supra-subduction zone setting.The chemical and textural variations in zoned chromite from chromitites and dunites can be interpreted in terms of a multistage process characterised by two episodes of retrograde metamorphism separated by a high-temperature heating event. This interpretation suggests a correlation with the tectono-metamorphic evolution of the Neoproterozoic basement of the Ossa-Morena zone.

Different varieties of serpentinites present at Cabo Ortegal were studied. For many years, the ‘Verde Pirineos’ type has been quarried and sold commercially, but its physical characteristics do not fulfil the requirements for its use as an ornamental stone. ‘Piedra de Doelo’ is the local name for a serpentinite that has been quarried and used for many centuries in a large number of historical buildings distributed throughout the area. The preservation status of the rock is very poor and the stone is severely affected by weathering. A third variety, similar to the ‘ophicalcite’ described in the literature, is currently under investigation with a view to studying the possibility of the resumption of serpentinite quarrying. Although serpentinites are commercially known as ‘green marbles’, Galician serpentinites do not fulfil the mineral requirements to be described as such. Study of the characteristics of serpentinites, including their mineralogy, may offer a clue to the correct use of Galician serpentinites.

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