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

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

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

Growth and post-growth defects in a natural diamond from Finsch mine (South Africa)

In recent years several studies were focused on the calculation of residual pressure around mineral inclusions in diamond in order to provide useful information on the depth of diamond origin. In these studies, the calculations were carried out using mainly vibrational spectroscopy data and were based on different assumptions including also the following important postulations: the diamond deforms elastically, no plastic or brittle deformation taking place during transportation to the surface, and the remnant pressure of the inclusion is the only cause of strain in the diamond that results in anomalous birefringence. [1] An helpful tool to verify the existence conditions of the aforementioned assumptions can be obtained by the analyses of structural defects using X-Ray Diffraction Topography (XRDT), a non-destructive imaging technique, sensitive to the strain associated with extended defects. This technique is particularly suitable for providing information about crystal growth and genetic environment of minerals by recording the spatial distribution of lattice defects and by the discrimination between growth and post-growth defects [2, 3, 4]. In this study a natural diamond from Finsch mine (South Africa) was investigated by XRDT in transmission geometry, using MoKα1 radiation with conventional source. The sample (F118) was a polished plate, about 1mm thick and cut perpendicular to [111]. The plate showed anomalous birefringence and a typical triangular shape with a rounded side in which re-entrant corners could be seen. X-ray topographs show that the sample is actually a mosaic crystal that developed through aggregation of individuals during growth: some slightly rotated relative to one another and others twinned. The twin law is by reticular merohedry and consists of the well-known 2-fold rotation around [111]. The larger inclusions are garnet crystals absorbed in the inner part of an individual showing triangular shape. No dislocations are nucleated from them. A number of inclusions were adsorbed at the interfaces between the twinned individuals and at the grain boundaries. Bundles of dislocations run from the smaller inclusions adsorbed in the outer region of the triangular individual. In the whole sample and chiefly in the regions showing a lower density of inclusions, packed lamination lines parallel to an octahedral face can be observed. These laminations represent a polysynthetic twinning commonly observed in diamonds when a plastic deformation occurs and thus can be considered post-growth defects. Finally, this study results useful to determine the strains associated to the inclusions and the presence of plastic deformation related to post-growth defects and thus can contribute to select the diamond samples and the inclusions suitable to provide information on the depth of diamond origin

X-ray diffraction topography of brown diamonds from Argyle and Udachnaya

Two crystals of brown diamonds, coming from Argyle and Udachnaya, were studied, in a non-destructive way, by means of X-Ray Diffraction Topography (XRDT) with the aim to elucidate the relationships between the structural defects and the growth history. The sample from Argyle mine, labelled Br11, was a light-brown diamond with an irregular tetrahedral morphology and free of inclusions. Br11 shows a complex intergrowth phenomenon: the analyses of the diffraction contrasts and the optical observations reveal that the sample is really formed by two individuals twinned by the well-known spinel law. These individuals, in turn, are formed by different sub-individuals with different orientation, piled up along the [111] direction. An aggregation of numerous and thick lamellae parallel to the triangular morphology of the (111) face characterizes each sub-individual. Moreover, the XRDT images show partial dissolution followed by a final overgrowth. The sample from Udachnaya, labelled Ud02, was a light-brown diamond with an octahedral morphology that exhibits several large inclusions and fractures partially healed by dark epigenetic microinclusions. The analyses of the diffraction contrasts of the Ud02 sample show extended deformation fields, growth bands parallel to the octahedral faces and, in addition, a micro-lamination parallel to (1-1-1) that across the whole sample irrespectively of the different growth sectors. These laminations represent a polysynthetic twinning commonly observed in diamonds, which have undergone plastic deformation and are considered post-growth defects (Agrosì et al., 2013). No dislocations nucleated from the inclusions were observed. The analysis of the structural defects allows a reconstruction of a complex growth history of these samples characterized by a sequence of alternating episodes of growth, dissolution and plastic deformation. Lastly, the common feature of the micro-laminations was related to the origin of brown colour