Backscattered Electron Images,Cathodoluminescence, and Raman Spectroscopy Study of Phosphates and Maskelynite from the H6 Cangas de Onís Regolith Breccia

A new study of the Cangas de Onís Regolith Breccia was performed to determine under CL, BSE, EDS/WDS, and Raman spectroscopy the nature and composition of the phosphates and maskelynite melts in this meteorite body. The new data provide evidence of at least two different maskelynitic glasses and the occurrence of various types of phosphates in the clasts and the matrix. This reveals a complex history of accretion and planetary reaccretion in this chondrite, suggesting two episodes of accretion.     

Role of pore structure in salt crystallisation in unsaturated porous stone

Laboratory driven crystallisation of sodium sulphate and sodium chloride from concentrated solution in unsaturated porous stones has been performed. This contributes to a better understanding of the mechanisms by which salts crystallise and as a consequence limit the durability of porous materials which has an impact on buildings, civil constructions, and historical monuments. The identification of minerals in porous materials has been performed by scanning electron microscopy (SEM), Environmental Scanning Electron Microscopy (ESEM) and sequential profiles of X-ray diffraction (XRD) under temperature control of sample. The study of porous stones has been combined with experiments in capillary tubes. Data from SEM show that halite tends to precipitate on the surface of the stone with a similar distribution in all samples. However, the mirabilite–thenardite precipitation takes place preferably inside the stone and its depth from the surface and its relative concentration depends on the pore size distribution. In addition, mirabilite (Na₂SO₄·10H₂O) crystallises homogeneously, whereas thenardite (Na₂SO₄) and halite (NaCl) tend to nucleate heterogeneously. To explain the precipitation sequence from concentrated solutions in unsaturated porous materials, a detailed analysis of the thermodynamic equations has been carried out by establishing a simple model. The proposed model shows the influence of the pore structure both on the water activity and saturation degree of involved salts.     

Influence of preheating treatment on the luminescence properties of adularia feldspar (KAlSi3O8)

During the firing of ceramics that contain alkali feldspar grains (up to 900°C in bricks and 1200°C in porcelains) the metastable equilibrium of these natural materials is altered (refractory minerals, neo-formed minerals and new glassy components). Hence, potassium rich feldspar lattices, which are being used in some routines of archaeological dating and retrospective dosimetry, suffer minor modifications by preheating and irradiation treatments (K-self-diffusion, stretching, etc.). In this paper, some pre-heatings of a K-feldspar (adularia) from Saint Gothard (Switzerland) attempted to simulate the temperatures and conditions undergone in brick manufacturing processes (1000°C for 24 h and 1200°C for 240 h). Some changes in the behavior of the TL and RL spectral curves were detected after combinations of thermal pretreatments (at 400°C for 48 h; 500°C for 72 h; 600°C for 96 h and 700°C for 144 h) and irradiations. Comparisons between high temperature annealed (1000 and 1200°C) and non-annealed adularias show spectacular changes in the shape of the TL glow curves: natural-irradiated adularia displays a single large peak at 100°C, whereas annealed adularias show a very complex structure. The observed modifications, probably due to thermal alkali self-diffusion through the lattice interfaces, tilting of the Al–Si crankshafts and phase exsolutions, have been detected by X-ray diffraction.