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Abstract: A UV laser has now been used to measure the Raman spectrum of lonsdaleite. This mineral species is a little-known hexagonal form of carbon having no known P–T field of stability. Lonsdaleite is known to coexist with diamond and/or graphite in certain impact structures and meteorites. Its presence in microinclusions in some ultrahigh-pressure eclogites is under discussion as there is a considerable wavenumber overlap of the sp 3 Raman band of lonsdaleite in the 1200–1400cm−1 region with certain bands of haematite, graphite and diamond, and also with “disordered-diamond” having a downshifted wavenumber. Various incoherent previously published values of the Raman bands are briefly reviewed and an attempt is made to establish a reference spectrum. Four samples of lonsdaleite from the Zapadnaya and Popigai impact structures (Ukraine) were measured with three different laser sources (488, 514.5 and 325nm) with two Raman spectrometers. UV-Raman was less fluorescent. All the new data were coherent in establishing an sp 3 band centred at 1324±4cm−1 with a FWHM about five times wider than that of diamond and an intensity about 500 times weaker. The presence of a second band giving a weak shoulder around 1225cm−1 is discussed with respect to the alternative of one continuous asymmetrical band. [Copyright &y& Elsevier]

Abstract: Raman microscopy (RM) is widely used in archaeometrical studies of pigments, geomaterials and biomaterials in the Cultural Heritage, but one domain has received relatively less attention: the colouring of stained glass. This feasibility study investigates the advantages and disadvantages of employing RM alone in this field by means of a study of modern commercial glasses, modern commercial pigments, and a few archaeological stained glasses, but especially by an experimental project whereby the authors created stained glass. The different kinds of possible unreacted or reacted material are rigorously established. The distinction between Na, K, Ca glasses was explored, as well as the red colouring of an industrial glass which was proved to be due to the presence of (Zn, Cd)S x Se1−x . Yellow, green, blue and maroon pigments were studied before and after an initial firing and then after heating on glass. The quality of the Raman spectra varied enormously and was sometimes disappointing. Nevertheless RM successfully identified various coloured products such as bindheimite, crocoite, cobalt aluminate, haematite; relict reactants such as corundum, eskolaite and oxides of Co or Pb; and provided indications of other phases such as maghemite or Co-olivine. One conclusion is that the amount of chemical reaction between the pigments and the glass is small compared to the amount in between the pigments. Comments are made on the potential for dating archaeological glass from the known age of synthesis of the pigments, and of the dangers of this approach. Overall it has been shown that RM can be useful for studying stained glass, especially for remote in situ analytical operations with mobile RM, but one must expect some problems either with fluorescence or weak spectra. [Copyright &y& Elsevier]

Abstract: The Kimi Unit of the Rhodope Metamorphic Province (RMP), NE Greece, experienced ultrahigh-pressure metamorphism (UHPM), as documented by the unequivocal presence of diamond microinclusions in metapelitic garnet porphyroblasts. Certain peculiar lozenge-shaped 2–8μm sized inclusions in diamond-bearing garnets reveal a broad composite and asymmetric triplet band (phase XXX) at ∼1331cm−1 in their Raman spectra acquired with a 632.8nm He–Ne laser, initially attributed to an sp3-hybridized C-polymorph. These have been meticulously re-investigated by means of combined 2-wavelength (514.5nm/632.8nm laser) Raman microscopy. Raman mapping has been extensively employed in order to examine the spatial distribution of phase XXX and of other phases in these polyphase inclusions and to explore for additional Raman bands. The triplet band at ∼1331cm−1 measured with the 632.8nm laser shifts to much higher wavenumbers (∼4966cm−1) when excited with a 514.5nm Ar+ laser, proving that the XXX triplet is not a real Raman band but a luminescence one at ∼691.1nm. Numerous hypotheses on the nature of the mysterious phase XXX (e.g. Cr3+-bearing mineral, carbonate, C polymorph, gas, organic phase) are explored and discussed but all are shown to be unsatisfactory. It is suggested that XXX occurs as nanocrystals that luminesce strongly giving the appearance (in Raman maps) of being larger. [Copyright &y& Elsevier]

Abstract: The “RAMANITA©” method, for semi-quantitative chemical analysis of mineral solid-solutions by multidimensional calibration of Raman wavenumber shifts and mathematical calculation by simultaneous equations, is published here in detail in English for the first time. It was conceived by the present writer 20 years ago for binary and ternary pyroxene and garnet systems. The mathematical description was set out in 1989, but in an abstract in an obscure French special publication. Detailed “step-by-step” calibration of two garnet ternaries, followed by their linking, by M. Pinet and D.C. Smith in the early 1990s provided a hexary garnet database. Much later, using this garnet database, which forms part of his personal database called RAMANITA©, the present writer began to develop the method by improving the terminology, automating the calculations, discussing problems and experimenting with different real chemical problems in archaeometry. Although this RAMANITA© method has been very briefly mentioned in two recent books, the necessary full mathematical explanation is given only here. The method will find application in any study which requires obtaining a non-destructive semi-quantitative chemical analysis from mineral solid solutions that cannot be analysed by any destructive analytical method, in particular for archaeological, geological or extraterrestrial research projects, e.g. [-] from gemstones or other crystalline artworks of the cultural heritage (especially by Mobile Raman Microscopy (MRM)) in situ in museums or at archaeological sites, including under water for subaquatic archaeometry; [-] from scientifically precious mineral microinclusions (such as garnet or pyroxene within diamond); [-] from minerals in rocks analysed in situ on planetary bodies by a rover (especially “at distance” by telescopy). Recently some other workers have begun deducing chemical compositions from Raman wavenumber shifts in multivariate chemical space, but the philosophical approach is quite different. [Copyright &y& Elsevier]

A series of laboratory simulations have been made in order to evaluate the credibility of carrying out physico-chemical analysis of cultural heritage items by Raman spectral fingerprinting using a mobile Raman microscope in situ under natural impure water in subaquatic or submarine conditions. Three different kinds of gemstone (zircon, microcline and sodalite) were successively placed under different kinds of impure water into which a low power microscope objective was immersed to eliminate the normal aerial pathway between the objective and the object to be analysed. According to the nature of the impurities (inorganic or organic, dissolved or suspended, transparent or coloured) the results obtained variously gave Raman band intensities stronger than, similar to or weaker than those of spectra obtained without water, i.e. in air. The significant point is that after only minor spectral treatment the less good spectra nevertheless yielded exploitable data with most, if not all, of the key Raman bands being detected. Thus the problems of fluorescence or peak absences under water are of a similar degree of magnitude to the other problems inherent with the Raman spectroscopic technique in aerial conditions, e.g. relative peak intensities varying with crystal orientation; peak positions varying with chemical composition. These results indicate that even if at certain sites of submerged cities or sunken ships, the combination of animal, vegetal, mineral and microbial impurities join together to inhibit or hinder the success of subaquatic or submarine archaeometry, there will certainly be other sites where such activity is indeed credible. [Copyright &y& Elsevier]