Ringwoodite, a cubic dimorph of olivine, has been synthesized under high pressure within 6-24 GPa, identified in products of a shock-wave experiment on two-mica-quartz schist, and found in six meteorites. In addition, Diaz-Martinez has reported ring-woodite from pumices of the El Gasco region, Spain. Therefore, the pumices were interpreted as impact-related formations on the basis of ringwoodite findings. The presence of ringwoodite in the pumices was confirmed by Diaz-Martinez using XRD data. Later works and the study of minerals and glasses on a Camscan 4DV microprobe equipped with an EDS Link AN 10000 allowed us to identify olivine-spinel intergrowths. This raised some doubts as to the presence of ringwoodite in these rocks. Ringwoodite and spinel have very similar X-ray characteristics, because ringwoodite actually represents olivine with a spinel structure. Therefore, XRD investigations cannot serve as reliable evidence for the presence of ringwoodite. In this connection, Diaz-Martinez discarded the impact origin of pumices and suggested that they can be related to artificial annealing. He believes that they represent the remains of ancient (Late Bronze Age) vitrified walls that consist of the pumices, which were obtained by melting of the host rocks (so-called vitrified forts), although they are localized beyond the artifact zone. No proponents remain for the previously accepted volcanic origin of the El Gasco pumice.
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