Bjørn Eske Sørensen

A revised Michel-Lévy interference colour chart based on first-principles calculations

Two revisions of the original Michel-Levy interference colour chart are presented, and discussed here. Compared to older charts these give a more precise match to the actual observations in the modern optical microscope. As an example, interference colour transitions on wedge shaped olivine grain boundaries toward epoxy match accurately the interference colour in the new charts. The differences in the colour between older charts and the new are most pronounced in the second order, where the saturated green is now replaced by greenish white and turquoise. In addition, the pinks are shown to cover a larger range than previously thought. The revised charts make it easier to determine interference colour and order, and hence also to determine the birefringence of the common silicate minerals. Because of the first-principle origin of the charts it is easy to adjust the charts for different types of optics and illumination. Also the improved understanding of interference colour opens up new possibilities in image analysis of transmitted-light images involving interference colour.

Late-magmatic immiscibility during batholith formation: assessment of B isotopes and trace elements in tourmaline from the Land’s End granite, SW England

Quartz–tourmaline orbicules are unevenly distributed in the roof segment of the Lands End granite, SW England. This study shows that the orbicules formed from an immiscible hydrous borosilicate melt produced during the late stages of crystallization, and differentiates tourmaline formed by dominantly magmatic and dominantly hydrothermal processes. Trace elements and boron isotope fractionation can be tracked in tourmaline, and create a timeline for crystallization. Tourmaline from the granite matrix has higher V, Cr and Mg content and is isotopically heavier than the later crystallizing inner orbicule tourmaline. Overgrowths of blue tourmaline, occurring together with quartz showing hydrothermal cathodoluminescence textures, crystallized from an aqueous fluid during the very last crystallization, and are significantly higher in Sr and Sn, and isotopically heavier. Tourmaline associated with Sn mineralization is also high in Sr and Sn, but has boron isotopic compositions close to that of the magmatic tourmaline, and is not formed by the same fluids responsible for the blue overgrowths. The ore-forming fluids precipitating tourmaline and cassiterite are likely derived from the same magma source as the granite, but exsolved deeper in the magma chamber, and at a later stage than orbicule formation. Tourmaline from massive quartz–tourmaline rocks is concentrically zoned, with major and trace element compositions indicating crystallization from a similar melt as for the orbicules, but shows a more evolved signature.

Assessment of Individual ASR-Aggregate Particles by XRD

This article describes the direct analysis of polished individual aggregate particles by X-ray diffraction (XRD), as compared to traditional powder samples. These particles are selected from mortar bars and concrete prisms previously exposed to expansion testing as well as virgin aggregate from the PARTNER project [1].The authors performed XRD analyses in solid and powder samples of the same aggregate particle. Comparing the results was concluded that for fine grained rocks without preferred orientation the use of a slab sample is more time efficient than traditional powder specimen, without compromising accuracy. Another advantage of this approach is that the investigated aggregate particles can be selected based on petrographic observations done in concrete thin sections affected by alkali-silica reaction (ASR).

Magma-driven, high-grade metamorphism in the Sveconorwegian Province, southwest Norway, during the terminal stages of Fennoscandian Shield evolution

Recently it has been argued that the Sveconorwegian orogeny in southwest Fennoscandia comprised a series of accretionary events between 1140 and 920 Ma, behind a long-lived, active continental margin characterized by voluminous magmatism and high-grade metamorphism. Voluminous magnesian granitic magmatism is recorded between 1070 and 1010 Ma (Sirdal Magmatic Belt, SMB), with an apparent drop in activity ca. 1010-1000 Ma. Granitic magmatism resumed ca. 1000-990 Ma, but with more ferroan (A type) compositions (hornblende-biotite granites). This ferroan granitic magmatism was continuous until 920 Ma, and included emplacement of an AMCG (anorthosite-mangerite-charnockite-granite) complex (Rogaland Igneous Complex). Mafic rocks with ages corresponding to the spatially associated granites suggest that heat from underplated mafic magma was the main driving force for lower crustal melting and long-lived granitic magmatism. The change from magnesian to ferroan compositions may reflect an increasingly depleted and dehydrated lower crustal source. High-grade metamorphic rocks more than similar to 20 km away from the Rogaland Igneous Complex yield meta-morphic ages of 1070-1015 Ma, corresponding to SMB magmatism, whereas similar rocks closer to the Rogaland Igneous Complex yield ages between 1100 and 920 Ma, with an apparent age peak ca. 1000 Ma. Ti-in zircon temperatures from these rocks increase from similar to 760 to 820 degrees C ca. 970 Ma, well before the inferred emplacement age of the Rogaland Igneous Complex (930 Ma), suggesting that long-lived, high-grade metamorphism was not directly linked to the emplacement of the latter, but rather to the same mafic underplating that was driving lower crustal melting. Structural data suggest that the present-day regional distribution of high-and low-grade rocks reflects late-stage orogenic doming.

Quantitative Mineral Characterization of Granitic Pegmatite Using Topas Rietveld XRD Refinement

A Topas Rietveld X-ray diffraction (XRD) method has been developed for granitic pegmatite using mineral structure to quantify the mineral content of the sample material. The prerequisite for successful Riteveld quantification is the correct input in terms of crystallographic information of the minerals tested. With this in mind the method presented here determine the content of the main minerals in a granitic pegmatite; quartz, soda-rich feldspar, potassium-rich feldspar, and biotite. The developed method has been tested against a semiquantitative combination method using XRD and X-ray fluorescence (XRF), and a normative calculation based on chemical results from XRF and electron probe microanalyzer (EPMA). The Topas Rietveld XRD method and the normative calculation produce consistent results, whereas the semiquantitative combination method using XRD and XRF produces incorrect and inconsistent results. The sample materials are products and raw materials from Sibelco Nordic and the quantitative Rietveld method is developed for use in mineral production quality control.