This article is dedicated to the memory of Professor Alfredo San Miguel . (Received 10 February 2005; revision accepted 24 March 2005)Abstract-An impressive daylight fireball was observed from Spain, Portugal, and the south of France at 16h46m45s UTC on January 4, 2004. The meteoroid penetrated into the atmosphere, generating shock waves that reached the ground and produced audible booms. The associated airwave was recorded at a seismic station located 90 km north of the fireball trajectory in Spain, and at an infrasound station in France located 750 km north-east of the fireball. The absolute magnitude of the bolide has been determined to be −18 ± 1 from a casual video record. The energy released in the atmosphere determined from photometric, seismic, and infrasound data was about 0.02 kilotons (kt). A massive fragmentation occurred at a height of 28 ± 0.2 km, resulting in a meteorite strewn field of 20 × 6 km. The first meteorite specimen was found on January 11, 2004, near the village of Villalbeto de la Peña, in northern Palencia (Spain). To date, about 4.6 kg of meteorite mass have been recovered during several recovery campaigns. The meteorite is a moderately shocked (S4) L6 ordinary chondrite with a cosmic-ray-exposure age of 48 ± 5 Ma. Radioisotope analysis shows that the original body had a mass of 760 ± 150 kg, which is in agreement with the estimated mass obtained from photometric and seismic measurements.

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ABSTRACT.-Two different types of ancient bricks (XII-XIVth centuries) collected from historical buildings of Toledo (Spain) were characterized by Optical Microscopy, SEM/EDS, Electron microprobe, XRD, DTA and 57 Fe-Mössbauer spectroscopy. Physical properties such as water absorption and suction, porosity, density and compression strength were also determined.Several minerals found in the brick matrix, such as garnet, let us infer raw material sources; calcite, dolomite, illite and neo-formed gehlenite and diopside phases, on temperature reached in firing; secondary calcite, on first cooling scenarios; and manganese micro-nodules, on late pollution environments. XRD and DTA of original and re-fired samples supply information about firing temperatures. Additional data on firing conditions and type of the original clay are provided by the Mössbauer study. Physical properties of both types of bricks were compared and correlated with raw materials and fabric and firing technology employed. The physicochemical characterization of these bricks provides valuable data for restoration purposes to formulate new specific bricks using neighbouring raw materials.

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The luminescence of synthetic rare earth (RE)-doped zircons and three natural zircons has been studied by ion beam excitation (ion beam luminescence or ionoluminescence (IL)). Luminescence results from electronic transitions between energy levels of the RE ions, giving emissions with characteristic energies. Studies of co-doped Ho : Dy zircon show that electronic cascades from Ho3+ to Dy3+ ions result in intense Dy3+ luminescence even when Ho is far more abundant. Dy3+ ions have the greatest luminescence cross-section of common RE3+ ions. Implantation of heavier N+ ions into zircon, chosen to mimic accelerated radiation-induced structural modification, causes significant sample degradation. Frenkel-type defects and groups in the zircon are associated with a broad luminescence band of ∼600 nm, and these defects modify energy cascades between RE3+ ions, thereby reducing the efficiency of energy deposition via the Dy3+ luminescence decay pathway. The broad band of ∼600 nm created by implantation is common in natural zircons and is attributed primarily to intrinsic Frenkel defects caused by natural radiation. Dy3+ luminescence is apparent from natural zircons even though Dy is one of the least abundant RE ions in zircon, and this behaviour is explained by the high luminescence cross-section of Dy3+ in zircon. Radiation-induced structural damage reduces the efficiency of energy transport between different RE3+ ions. IL provides key insights into both the interactions between defects and the nature of luminescence centres in zircon.

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The aim of this work was to determine the type of weathering suffered by bricks belonging to a number of historic buildings in Toledo, Spain. These bricks had been exposed to either aerial or burial environments, came from different places in the selected buildings, were of different mineralogical composition, and had been fired at different temperatures. X-ray diffraction, scanning electron microscopy and the analysis of their physical properties showed the best conserved to be those that had been buried. Buried Roman bricks made from non-calcareous materials fired at 4900 1C and with a vitrified matrix showed few signs of weathering. Buried Islamic and Mudejar-Romanesque bricks made from calcareous clays and fired at temperatures of o800 1C were similarly well conserved. These showed calcareous cementation of their pore systems, which improved their physical properties. Bricks from the external and internal walls of buildings (e.g., Islamic-Mudejar and Romanesque bricks from inner courtyards and cellars) that had been exposed to aerial conditions were less well conserved. These were made from calcareous materials and had been fired at high temperatures (4900 1C). They showed a number of weathering traces but overall were still in relatively good condition. The worst conserved of all were neoclassical bricks from upper storey internal walls. These were made of calcareous material and had been fired at temperatures of between 800 and 900 1C.The mineralogical composition of the raw materials, the firing temperature, the location of the bricks in the buildings, the environments to which they had been exposed, the action of natural or polluted filtration water, the action of microorganisms and the reigning environmental conditions, all contributed towards the state of conservation of the bricks. Such knowledge may help in the choice of appropriate cleaning or restoration treatments for architectural heritage of brick construction. r