Open Access

Show Abstract ▼

Abstract: Purportedly originating from the late Predynastic–Early Dynastic period of ancient Egyptian civilisation (about 3100 BC), the statuette known as “MacGregor Man” was acquired near the site of Naqada in southern Egypt by the Reverend William MacGregor at the end of the 19th century. The Ashmolean Museum (University of Oxford) subsequently purchased the statuette at the sale of MacGregor’s collection in 1922, and it remains one of the most important items in the museum’s Egyptology collection. However, the authenticity of the statuette has been the focus of fierce scholarly debate since it first came to light. At that time there was little with which the object could be compared and a forger would have little source material to copy: some of its features are consistent with securely provenanced statuettes and figurines that were discovered some time after the appearance of MacGregor Man. Several other aspects have caused others to question whether MacGregor Man is genuine. It is carved from what is widely believed to be a basaltic rock; rare in ancient Egypt and its hardness would have made sculpting such a detailed statue exceedingly difficult with the tools available to ancient stonemasons. Also, there are strong indications that MacGregor Man may have been deliberately damaged, possibly in an effort to artificially “antiquate” the statuette (though other explanations are feasible). Despite the sustained interest in MacGregor Man, no mineralogical analysis of the stone it is sculpted from has been carried out to date. Though it has been visually identified as being most likely a basalt, it has so far been impossible to ascertain even this basic information without removing a sample from and thus damaging the statue. Even a basic understanding of the mineralogy of the sample could prove informative since basaltic composition can be diagnostic for determining the region of its origin. Using energy-dispersive X-ray diffraction (EDXRD) in a back-reflection geometry, a non-destructive technique, high-resolution powder diffraction data from several regions were collected at Diamond Light Source (Didcot, Oxfordshire, U.K.) in February 2019. From these data, despite poor powder averaging (resulting from the large crystallite size), we plan to extract crystallographic information such as the minerals present and unit cell dimensions. This will be compared to published data from known Egyptian basalt samples in an attempt to ascertain whether it is Egyptian in origin. The results of this crystallographic analysis will be presented.

Open Access

Show Abstract ▼

Abstract: The mineralogy of comet 81P/Wild 2 particles, collected in aerogel by the Stardust mission, has been determined using synchrotron Fe-K X-ray absorption spectroscopy with in situ transmission XRD and X-ray fluorescence, plus complementary microRaman analyses. Our investigation focuses on the terminal grains of eight Stardust tracks: C2112,4,170,0,0; C2045,2,176,0,0; C2045,3,177,0,0; C2045,4,178,0,0; C2065,4,187,0,0; C2098,4,188,0,0; C2119,4,189,0,0; and C2119,5,190,0,0. Three terminal grains have been identified as near pure magnetite Fe3O4. The presence of magnetite shows affinities between the Wild 2 mineral assemblage and carbonaceous chondrites, and probably resulted from hydrothermal alteration of the coexisting FeNi and ferromagnesian silicates in the cometary parent body. In order to further explore this hypothesis, powdered material from a CR2 meteorite (NWA 10256) was shot into the aerogel at 6.1 km s−1, using a light-gas gun, and keystones were then prepared in the same way as the Stardust keystones. Using similar analysis techniques to the eight Stardust tracks, a CR2 magnetite terminal grain establishes the likelihood of preserving magnetite during capture in silica aerogel.

Open Access

Show Abstract ▼

Abstract: Energy-dispersive X-ray diffraction (EDXRD) implemented in a back-reflection geometry is extremely insensitive to sample morphology and positioning even in a high-resolution configuration1,2. This technique allows high-quality XRD analysis of samples that have not been prepared in any way and is therefore completely non-destructive. The experimental technique was implemented on beamline B18 at the Diamond Light Source synchrotron in Oxfordshire, UK. The majority of the experiments in this study were performed with pre-characterised geological materials in order to elucidate the characteristics of this novel technique and to develop the analysis methods. Sample d-spacings were extracted from the data with a typical accuracy of 2 x 10-4 Å, enabling phase identification and the derivation of precise unit-cell parameters which yield insights into the sample material such as the position within a solid solution series. The data is of sufficient quality to allow the investigation of microstructural properties such as crystallite size and shape, and microstrain. A particular highlight was the identification of a specific polytype of a muscovite in an unprepared mica schist sample, avoiding the time-consuming and difficult preparation steps normally required to make this type of identification in a phyllosilicate-containing sample. The technique was also demonstrated in application to a small number of fossil and archaeological samples, including a Cretaceous shark tooth and a Roman glass mosaic tessera; details of these analyses will be given in the presentation. Back-reflection EDXRD implemented in a high-resolution configuration shows great potential in the crystallographic analysis of cultural heritage artefacts and other specimens. Scientific research of archaeological objects is usually conducted either for the purposes of provenancing or as an aid to the formulation of effective conservation strategies. The avoidance of the need to extract samples from high-value and rare objects is a highly-significant advantage, applicable in other potential research areas such as palaeontology, and the study of meteorites and planetary materials brought to Earth by sample-return missions. References 1. G. M. Hansford, “Back-Reflection Energy-Dispersive X-Ray Diffraction: A Novel Diffraction Technique with Almost Complete Insensitivity to Sample Morphology”, J. Appl. Cryst., 44, 514-525 (2011). 2. G. M. Hansford, S. M. R. Turner, P. Degryse and A. J. Shortland, “High-resolution X-ray diffraction with no sample preparation”, Acta Cryst. A73, 293-311 (2017).

Show Abstract ▼

Abstract: Energy-dispersive XRD (EDXRD) applied in the back-reflection geometry, with 2θ close to 180°, is extremely insensitive to sample morphology1. This property enables analysis with no sample preparation and is therefore entirely non-destructive, allowing high-quality XRD analysis of valuable samples such as archaeological artefacts with no compromise to the integrity of the object whatsoever.

Show Abstract ▼

Abstract: The identification of saponite and amorphous material in the Sheepbed mudstone of Gale Crater by CheMin XRD on Mars Science Laboratory [1] has highlighted the importance of understanding the nature of martian phyllosilicates and amorphous material, as they have the potential to reveal the fluid history of habitable terrains [2,3]. The nakhlite meteorites are the only martian samples on Earth which contain phyllosilicates and poorly crystalline or amorphous material [4-10], which we can study by new XRD and X-ray Absorption techniques and TEM to provide an accurate Fe3+/ΣFe ratio, composition and structural comparison to the in situ analyses on Mars.