| 1. |
- Lastusaari, Mika, et al.
(författare)
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The Bologna Stone: history's first persistent luminescent material
- 2012
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Ingår i: European Journal of Mineralogy. - : Schweizerbart. - 1617-4011 .- 0935-1221. ; 24:5, s. 885-890
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Tidskriftsartikel (refereegranskat)abstract
- In 1603, the Italian shoemaker Vincenzo Cascariolo found that a stone (baryte) from the outskirts of Bologna emitted light in the dark without any external excitation source. However, the calcination of the baryte was needed prior to this observation. The stone later named as the Bologna Stone was among the first luminescent materials and the first documented material to show persistent luminescence. The mechanism behind the persistent emission in this material has remained a mystery ever since. In this work, the Bologna Stone (BaS) was prepared from the natural baryte (Bologna, Italy) used by Cascariolo. Its properties, e. g. impurities (dopants) and their valences, luminescence, persistent luminescence and trap structure, were compared to those of the pure BaS materials doped with different (transition) metals (Cu, Ag, Pb) known to yield strong luminescence. The work was carried out by using different methods (XANES, TL, VUV-UV-vis luminescence, TGA-DTA, XPD). A plausible mechanism for the persistent luminescence from the Bologna Stone with Cu+ as the emitting species was constructed based on the results obtained. The puzzle of the Bologna Stone can thus be considered as resolved after some 400 years of studies.
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| 2. |
- Chukanov, Nikita V., et al.
(författare)
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Långbanshyttanite, a new low-temperature arsenate mineral with a novel structure from Långban, Sweden
- 2011
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Ingår i: European journal of mineralogy. - : Schweizerbart. - 0935-1221 .- 1617-4011. ; 23:4, s. 675-681
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Tidskriftsartikel (refereegranskat)abstract
- The new mineral långbanshyttanite was discovered in a specimen from the Långban mine (59.86 degrees N, 14.27 degrees E), Filipstad district, Varmland County, Bergslagen ore province, Sweden. Associated minerals are calcite, Mn-bearing phlogopite, spinels of the jacobsite-magnetite series, antigorite and trigonite. The mineral is named after the old name of the mine, smelter and mining village: Långbanshyttan. Långbanshyttanite is transparent, colourless. It occurs in late-stage fractures or corroded pockets, forming soft, radial and random aggregates (up to 1 mm) of acicular crystals up to 5 x 20 x 400 mu m. D(calc) is 3.951 g/cm(3). The new mineral is biaxial (+), alpha = 1.700(5), beta = 1.741(5), gamma = 1.792(5), 2V (meas.) approximate to 90 degrees, 2V (calc.) = 86 degrees. Dispersion is strong, r < v. The IR spectrum is given. The chemical composition is (electron microprobe, mean of five analyses, wt%): PbO 44.71, MgO 3.79, MnO 13.34, FeO 1.89, P(2)O(5) 0.65, As(2)O(5) 22.90, H(2)O (determined by gas chromatographic analysis of the products of ignition at 1200 degrees C) 14.4; total 101.68. The empirical formula based on 18 O atoms is: Pb(1.97)Mn(1.85)Mg(0.93)Fe(0.26)(AsO(4))(1.96)(PO(4))(0.09)(OH)(3.87)cen ter dot 5.93H(2)O. The simplified formula is: Pb(2)Mn(2)Mg(AsO(4))(2)(OH)(4)center dot 6H(2)O. Single-crystal diffraction data obtained using synchrotron radiation indicate that långbanshyttanite is triclinic, P<(1)over bar>, a = 5.0528(10), b = 5.7671(6), c = 14.617(3) angstrom, alpha = 85.656(14), beta = 82.029(17), gamma = 88.728(13)degrees, V = 420.6(2) angstrom(3), Z = 1, and is a representative of a new structure type. In the structure, edge-sharing MnO(2)(OH)(4) octahedra form zig-zag columns that are linked by isolated AsO(4) tetrahedra. Pb cations having six-fold coordination are located between the AsO(4) tetrahedra. Isolated Mg(H(2)O)(6) octahedra are located in the inter-block space. The strongest lines of the powder diffraction pattern [d, angstrom (I,%) (hkl)] are: 14.48 (100) (001), 7.21 (43) (002), 4.969 (34) (100, 101), 4.798 (28) (003), 3.571 (54) (112, 1-1-1, 01-3, 11-1), 2.857 (45) (020, 021, 114), 2.800 (34) (11-3). Parts of the holotype specimen are deposited in the Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow, Russia, with the registration number 4032/1 and in the collections of the Swedish Museum of Natural History, Stockholm, Sweden, under catalogue number NRM 20100076.
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| 3. |
- Perdikouri, Christina, et al.
(författare)
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Hydrothermal replacement of Aragonite by Calcite : interplay between replacement, fracturing and growth
- 2013
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Ingår i: European journal of mineralogy. - : Schweizerbart. - 0935-1221 .- 1617-4011. ; 25:2, s. 123-136
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Tidskriftsartikel (refereegranskat)abstract
- The hydrothermal transformation of single aragonite crystals into polycrystalline calcite has been studied under hydrothermal conditions. The transformation involves a fluid-mediated replacement reaction, associated with fracturing of the initial aragonite crystal and growth of calcite throughout various parts of the reacted aragonite. The observed overall preservation of the crystal morphology is typical of an interface-coupled dissolution-reprecipitation mechanism Analysis of the crystallographic orientation of the product calcite using electron backscatter diffraction (EBSD) showed little to no link between the two phases under the studied conditions, with calcite crystallites exhibiting dominantly different crystallographic orientations compared to those of the aragonite and of neighbouring calcite domains. The complexity of the observed textures is mainly a result of the combination of fracturing of the crystal and initiation of nucleation and growth at different points of the exposed aragonite surface. Experiments performed with solutions enriched in O-18 as a tracer for oxygen exchange and monitored by Raman spectroscopy, showed that carbonate ions in the starting solution are mixed with carbonate from the dissolving aragonite, resulting in an O-18 concentration in the product calcite which depended on the local fluid transport through the fractures. As replacement processes among the CaCO3 phases are relevant to a wide range of applications, understanding the mechanisms is essential for the interpretation of observations of natural and/or experimental samples. This study describes the interplay between the replacement process, the fracturing of the crystal and growth of the new phase, calcite, and provides new insights into the mechanism of the aragonite to calcite transition. The combination of the two methods, EBSD and Raman spectroscopy, demonstrates the importance of local fluid composition and transport pathways in determining the isotope and element exchange in mineral replacement reactions.
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| 4. |
- Mohammad, Y O, 7602, et al.
(författare)
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Mg-staurolite and kyanite inclusions in metabasic garnet amphibolite from the Swedish Eastern Segment: evidence for a Mesoproterozoic subduction event.
- 2011
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Ingår i: European Journal of Mineralogy. - 0935-1221. ; 23:4, s. 609-631
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Tidskriftsartikel (refereegranskat)abstract
- We present evidence that the 1674 Ma Bora°s Mafic Intrusion of the Swedish Eastern Segment experienced high-pressure metamorphism related to a Sveconorwegian subduction-exhumation cycle. Mg-rich staurolite is found as inclusions in garnet in metaluminous amphibolites. The inclusion assemblages include staurolite (XMg 0.34–0.40), kyanite, euhedral anorthite, clinozoisite and quartz. The thermodynamic packages winTWQ and Theriak-Domino were used to investigate the P-T conditions of the matrix and inclusion mineral parageneses. The bulk composition of the rock does not have a stability field for staurolite-bearing parageneses. In our samples minerals of an eclogite-facies paragenesis became isolated from the whole rock in the first stage as inclusions in garnet. High Zn levels in the staurolite (0.6–1 wt% ZnO) show that it must have formed as either chloritoid or staurolite, both of which concentrate Zn. Euhedral anorthite inclusions have trace-element compositions including high Sr and insignificant Eu anomalies, which support their interpretation as pseudomorphs after lawsonite in plagioclase-out conditions. Rutile lamellae in the garnet are also indicative of a high-pressure origin. Calculated phase diagrams show that the most likely original paragenesis was garnet þ clinopyroxene þ Mg-rich chloritoid þ lawsonite þ kyanite þ quartz, which has a stability field for the whole-rock composition at 600 °C and 2.23–2.45 GPa. These conditions correspond to depths greater than 75 km, thus the Bora°s Mafic Intrusion was situated in the mantle at that time, implying subduction of the crustal block in which it was situated. The minerals now observed in the inclusions and in the rock matrix formed under amphibolite-facies conditions at lower pressures of 0.6–0.9 GPa and slightly increased temperatures around 650 °C, reflecting rapid exhumation from the mantle. Sm-Nd dating of garnet gives 957.1 ° 9.4 Ma, consistent with less precise Lu-Hf data, and represents either garnet growth during subduction or resetting during exhumation. Our investigations of staurolite in amphibolites documented in the literature show that staurolite cannot form in equilibrium with amphibolitefacies parageneses in normal metabasic rocks, which always have metaluminous compositions. A two-stage process is required in which a peraluminous assemblage with kyanite and possibly chloritoid first forms, due to plagioclase-out reactions in eclogite-facies conditions. Staurolite forms in the second stage during exhumation as pressure decreases, in domains which are not in contact with the common amphibolite-facies assemblage, for example by hydration reactions involving kyanite and garnet or by breakdown of chloritoid at higher temperatures. The pressures estimated for garnet growth and the development of inclusions correspond to minimum depths of 75–83 km (for basaltic or granitic overburden) and the Bora°s Mafic Intrusion is an integral part of the Eastern Segment in which retrograde eclogite metabasic bodies occur within orthogneisses in at least four other localities. This implies that a major part of the Eastern Segment experienced a high-pressure metamorphic event and the entire block of continental crust was involved in a subduction-exhumation cycle during the Sveconorwegian orogeny.
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| 5. |
- Viridén, Anna, 1977, et al.
(författare)
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Release of theophylline and carbamazepine from matrix tablets - Consequences of HPMC chemical heterogeneity
- 2011
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Ingår i: European Journal of Mineralogy. - : Elsevier BV. - 0935-1221. ; 78:3, s. 470-479
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Tidskriftsartikel (refereegranskat)abstract
- The release of theophylline and carbamazepine from matrix tablets composed of microcrystalline cellulose, lactose and hydroxypropyl methylcellulose (HPMC) was studied. The aim was to investigate the effect of different substituent heterogeneities of HPMC on the drug release from matrix tablets composed of either 35% or 45% HPMC. The release of the poorly soluble carbamazepine was considerably affected by the HPMC heterogeneity, and the time difference at 80% drug release was more than 12 h between the formulations of different HPMC batches. This was explained by slower polymer erosion of the heterogeneous HPMC and the fact that carbamazepine was mainly released by erosion. In addition, results from magnetic resonance imaging showed that the rate of water transport into the tablets was similar. This explained the comparable results of the release of the sparingly soluble theophylline from the two formulations even though the polymer erosion and the swelling of the tablets were considerably different. Thus, it can be concluded that the drug release was highly affected by the substituent heterogeneity, especially in the case of carbamazepine, which was released mainly by erosion. (C) 2011 Elsevier B.V. All rights reserved.
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