A new mineral with an olivine structure and pyroxene composition in the shock-induced melt veins of Tenham L6 chondrite
Abstract
We report a new mineral that occurs in shock-induced melt veins of the Tenham L6 chondrite. The new mineral, identified by transmission electron microscopy (TEM), occurs as acicular nanocrystals in a glassy matrix at the edge of shock-induced melt veins that crystallized during rapid quench at high pressure. The elongate crystals have aspect ratios up to 25. Widths range from -5 to -40 nm and lengths are up to 500 nm. Energy-dispersive X-ray spectroscopy (EDS) analyses provide the relative cation abundances that are consistent with a pyroxene-like stoichiometry: Na0.06Ca0.02Mg0.71Fe0.20Al0.11Si0.94O3. Selected area electron diffraction (SAED) patterns from single-crystal and polycrystalline aggregates indicate an olivine structure with refined cell parameters: a = 4.78, b = 10.11, and c = 5.94 Å and a calculated density of 3.32 g/cm3. Synchrotron X-ray microdiffraction data are consistent with an olivine structure and provide similar cell parameters: a = 4.778, b = 10.267, c = 5.937 Å. The pyroxene composition represents a large deviation from olivine stoichiometry, (Na0.08Ca0.03Mg0.95 Fe0.26Al0.15Si0.25□0.28)2Si1O4, with 0.28 formula units of vacancies (□), 0.11 of Na+ plus Ca2+, and 0.25 of Si4+, in octahedral sites. Our observations indicate that a metastable and nonstoichiometric olivine structure can crystallize from a silicate melt during rapid quench. Trace amounts of such defects may be present in stable olivines in the deep upper mantle
© 2015 by Walter de Gruyter Berlin/Boston
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Artikel in diesem Heft
- Paulscherrerite from the Number 2 Workings, Mount Painter Inlier, Northern Flinders Ranges, South Australia: “Dehydrated schoepite” is a mineral after all
- Atomistic investigation of the pyrophyllitic substitution and implications on clay stability
- Application of the two-feldspar geothermometer to ultrahigh-temperature (UHT) rocks in the Khondalite belt, North China craton and its implications
- Wüstite in a hydrothermal silver-lead-zinc vein, Lucky Friday mine, Coeur d’Alene mining district, U.S.A.
- Gelosaite, BiMo6+(2–5x)Mo5+6xO7(OH)·H2O (0 ≤ x ≤ 0.4), a new mineral from Su Senargiu (CA), Sardinia, Italy, and a second occurrence from Kingsgate, New England, Australia
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- Ultra-high residual compressive stress (>2 GPa) in a very small volume (<1 μm3) of indented quartz
- Transmission electron microscopy investigation of Ag-free lillianite and heyrovskýite from Vulcano, Aeolian Islands, Italy
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- The high-temperature P21/m → C2/m phase transitions in synthetic amphiboles along the richterite–(BMg)–richterite join
- The crystal structure of barite, BaSO4, at high pressure
- Thermal decomposition of brushite, CaHPO4·2H2O to monetite CaHPO4 and the formation of an amorphous phase
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- High-pressure structural evolution and equation of state of analbite
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- Synthesis and characterization of françoisite-(Nd): Nd[(UO2)3O(OH)(PO4)2]·6H2O
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- Acid production by FeSO4·nH2O dissolution: Comment
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