micro-LIBS vs. XRF analysis of surface-enriched silver coins. Is a micro-destructive approach really unavoidable?

We have performed a comparative study of micro-LIBS and X-Ray Fluorescence Spectroscopy (XRF) analysis for quantifying the silver contents in Swabian deniers minted during the Kingdom of Sicily (1194-1266). The combined use of the two techniques allowed us to validate the chemical composition of the coins and to valuate the altered surface and the surface-enrichment treatment eventually undergone. The use of LIBS coupled with microscope allowed to reduce the dimen- sion of the laser-induced crater below 20μm so the visual aspect of the coin remains unchanged. The LIBS measures over- come the question of the surface alteration, but they do not represent the heterogeneity of the alloy because of the small sampling area. On the other hand, the XRF technique allows to analyze a larger surface, in a totally non destructive way; however, the sampling volume could be affected by alterations or excessive roughness. It has been verified that these two factors do not affect the reliability of the measures but could introduce an uncertainty in the quantity data. The LIBS quanti- tative data have been obtained using the One Point Calibration method (OPC) while the XRF quantitative data were ob- tained by means of the Fundamental Parameter method. A good agreement between the two results was found, demonstrat- ing the effectiveness of both the micro-LIBS and XRF techniques, in spite of the above mentioned limitations. The compara- tive study has been conducted on a group of 50 deniers belonging to the reign of Henry VI and Frederick II; the results con- firmed the knowledge about the devaluations of the coins within 50 years of the Swabian Kingdom. A classification method has been proposed to set historically the coins

An Innovative Approach to Meteorite Analysis by Laser-Induced Breakdown Spectroscopy (LIBS)

An innovative approach of double pulse laser-induced breakdown spectroscopy (DP-LIBS) coupled with optical microscopy was applied to the characterisation and quantitative analysis of the Agoudal iron meteorite in bulk sample and in petrographic thin section. Qualitative analysis identified the elements Ca, Co, Fe, Ga, Li and Ni in the thin section and the whole meteorite. Two different methods, calibration-free LIBS and one-point calibration LIBS, were used as complementary methodologies for quantitative LIBS analysis. The elemental composition data obtained by LIBS were in good agreement with the compositional analyses obtained by traditional methods generally applied for the analysis of meteorites, such as ICP-MS and EDS-SEM. Besides the recognised advantages of LIBS over traditional techniques, including versatility, minimal destructivity, lack of waste production, low operating costs, rapidity of analysis, availability of transportable or portable systems, etc., additional advantages of this technique in the analysis of meteorites are precision and accuracy, sensitivity to low atomic number elements such as Li and the capacity to detect and quantify Co contents that cannot be obtained by EDS-SEM

Micro-imaging VIS-IR spectroscopy of Martian meteorites in support of the future MaMIss spectrometer measurements

In the view of the future ExoMars 2020 mission, an activity of VIS-IR spectral investigations on terrestrial and extraterrestrial Mars Analogues is ongoing, in support of the Ma Miss in situ measurements. Ma_Miss is an imaging spectrometer that works in the range 0.4-2.2 μm with 20nm spectral sampling and that will observe the lateral wall of the borehole generated by ExoMars Rover's drill (Coradini et al., 2001). In this abstract, we describe some results about the spectral properties and characterization of mineral grains of the slabs of two Martian meteorites by means of the SPIM imaging spectrometer. SPIM works in the 0.22-5.05 μm spectral range, with a spatial resolution of 38x38 μm on the sample and represents the spare of the spectrometer on Dawn spacecraft (De Angelis et al., 2015). The meteorites investigated are North West Africa 8657 (NWA8657) and Dar Al Gani 489 (DAG489), basaltic shergottites. The average spectrum of the NWA8657 slab, in comparison with spectral measurements on other martian meteorites (Mcfadden & Cline, 2005) shows low reflectance values and 1 and 2 μm spectral absorptions indicating the strong presence of Ca-pyroxenes. The successive pixel by pixel analyses for the pyroxenes spectral speciation showed a great variability of clinopyroxenes in NWA8657. In fact, the 2 μm absorption at longer wavelength in some pixel does not always correspond to the 1 μm feature at longer wavelength. The average spectrum of DAG 489 is marked by a signature typical of low-Ca pyroxenes. Pixel by pixel analyses of DAG489 shows a more homogeneous composition of the pyroxenes characterized by the two major features centered at 0.98-0.99 and 1.98-2 μm. Further spectral absorptions related to sulfates, phosphates and carbonates were detected that are being validated by SEM-BSD to constrain the formation hystories of these two shergottites

Fe-rich ferropericlase and magnesiow\ufcstite inclusions reflecting diamond formation rather than ambient mantle

At the core of many Earth-scale processes is the question of what the deep mantle is made of. The only direct samples from such extreme depths are diamonds and their inclusions. It is commonly assumed that these inclusions reflect ambient mantle or are syngenetic with diamond, but these assumptions are rarely tested. We have studied inclusion\u2013host growth relationships in two potentially superdeep diamonds from Juina (Brazil) containing nine inclusions of Fe-rich (XFe 480.33 to 650.64) ferropericlase-magnesiow\ufcstite (FM) by X-ray diffractometry, X-ray tomography, cathodoluminescence, electron backscatter diffraction, and electron microprobe analysis. The inclusions share a common [112] zone axis with their diamonds and have their major crystallographic axes within 3\ub0\u20138\ub0 of those of their hosts. This suggests a specific crystallographic orientation relationship (COR) resulting from interfacial energy minimization, disturbed by minor post-entrapment rotation around [112] due to plastic deformation. The observed COR and the relationships between inclusions and diamond growth zones imply that FM nucleated during the growth history of the diamond. Therefore, these inclusions may not provide direct information on the ambient mantle prior to diamond formation. Consequently, a \u201cnon-pyrolitic\u201d composition of the lower mantle is not required to explain the occurrence of Fe-rich FM inclusions in diamonds. By identifying examples of mineral inclusions that reflect the local environment of diamond formation and not ambient mantle, we provide both a cautionary tale and a means to test diamond-inclusion time relationships for proper application of inclusion studies to whole-mantle questions

Standardless, minimally destructive chemical analysis of red beryls by means of Laser Induced Breakdown Spectroscopy

Laser Induced Breakdown Spectroscopy (LIBS) is a valuable technique for performing qualitative and quantitative chemical analyses of all elements in one shot, including light elements (like Li and Be). This technique does not require any sample preparation and reveals all atomic species, even when present in small amounts. In this study we use a new LIBS prototype coupled with a petrographic microscope to obtain a spot size of approximately 10 μm on selected and homogeneous areas with minimal damage to the mineral. Qualitative and quantitative chemical analyses were performed on six samples of a rare red variety of beryl, using a standardless method (Calibration Free-LIBS) for quantitative data. Preliminary analyses by Raman spectroscopy and VIS-NIR reflectance spectroscopy showed that two of the six samples were pezzottaite. The LIBS spectra confirm the Raman and VIS-NIR data, demonstrating that this technique can distinguish red beryl from pezzottaite, mainly by observing the differences in Cs and Li emission lines. The standardless quantitative analysis proves to be suitable for the quantification of major and minor elements in beryl, as shown by comparison with literature data. In particular, the quantification of Mn confirmeda direct correlation between the concentration of this chromophore element and the red colour saturation of the sample

Crystal Chemical Characterisation of Red Beryl by "Standardless" Laser Induced Breakdown Spectroscopy and Single Crystal Refinement by X‐Ray Diffraction: An Example of Validation of an Innovative Method for the Chemical Analyses of Minerals

Laser induced breakdown spectroscopy (LIBS) is a valuable technique for performing qualitative and quantitative chemical analyses of all elements in one shot, including low atomic number elements such as Li and Be. This technique does not require any sample preparation to reveal the atomic species, even when present in trace amounts (< 0.01% m/m ). In this study, for the first time, we provide an accurate mineral formula for a Cs‐rich red beryl by combining crystallographic data obtained using the traditional single‐crystal X‐ray diffraction technique and quantitative chemical analysis data obtained with an innovative "standardless" method: Calibration Free‐LIBS (CF‐LIBS). In particular, a new LIBS prototype coupled with a petrographic microscope (CF‐μLIBS) was used to analyse chemically homogeneous areas of about 10 μm spot size, causing minimal damage to the mineral. The results showed that calibration‐free quantitative analysis is suitable for the quantification of major and minor low and high atomic number elements in beryl. The accuracy of quantification of low atomic number elements by CF‐μLIBS led to the empirical formula: [12](Cs0.006Na0.019K0.017Ca0.019)Σ0.061 [4](Be2.989Li0.011)Σ3.000 [6](Ti0.053Mn0.051Mg0.007Al1.890)Σ2.000 [4](Be0.116Fe0.024Si5.860)Σ6.000 O18. This formula is consistent with the crystal‐structure refinement data and demonstrates the validity of CF‐μLIBS for chemical analyses of minerals containing low atomic number elements

Growth Defects of titanian-andradite crystals from Colli Albani (Italy)

Growth defects and chemical zonings of Ti-rich andradite (melanite) crystals from Colli Albani were studied using X-ray Diffraction Topography and Electron Probe Microanalysis in order to determine the distinctive features, “growth marks”, characterising minerals grown directly from high temperature solution in an open system (volcanic chamber). The samples, cut in (110) and (001) slices, showed a number of primary and, above all, multiphasic melt inclusions, as well as, an unusual colour zoning consisting of a darker colour in the {211} growth sectors with the respect to the {110} sectors. The analysis of X-ray topographic contrasts of growth defects as growth bands, sector boundaries and bundles of dislocations developed parallel to the growth directions has enabled the reconstruction of the morphological evolution vs. time of the samples. The results also suggest that from their onset the crystals were faceted with {211}and predominant {110} faces. Moreover, the topographic images indicated that most of the examined dislocations were nucleated from inclusions. By using the extinction criterion, it was possible to determine that these defects are characterised by a strong edge component. The faceted morphology of garnets found in this paper and the fact that edge dislocations were only characterised suggest a layer spreading growth mechanism by two-dimensional nucleation. The reconstruction of morphology was also particularly useful in distinguishing two different types of chemical zoning: concentric and sector zoning. The results of chemical analyses confirmed that the optically observed colour zoning coincided with sector zoning because of a small but meaningful enrichment of TiO2 and a decrease of Al2O3 in correspondence with {211} growth sectors. Instead, concentration variations, chiefly of TiO2 and SiO2, were recorded crossing successive growth stages. This event appeared to be associated with the physio-chemical evolution of the growth environment and was defined as concentric zoning. Comparing the results found in our study with those of previous studies on garnets from hydrothermal and metasomatic environments, the meaning of the growth marks in the Ti-rich andraditic garnets from Colli Albani could be assigned to primary multiphase melt inclusions, concentric and sector zoning, sector boundaries, growth bands and edge dislocations since these defects characterise and distinguish our samples from those grown in different genetic environments