TEM investigation of Ca-rich plagioclase: Structural fluctuations related to the IFormula-PFormula phase transition

Németh, Péter; Tribaudino, Mario; Bruno, E.; Buseck, Peter R.

doi:10.2138/am.2007.2504

Cited by 10 publications

(12 citation statements)

References 21 publications

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“…6c, utilizing a pair of e-satellites for dark-field imaging, additional ∼ 50 nm domains with diffuse boundaries are visible only in the Ca-rich lamellae; however, none were found in the Ca-poor lamellae. These could have been formed during the phase transition from the high-temperature C1 phase to the low-temperature e-plagioclase, similar to experimental results of Benna et al (1995) and Németh et al (2007) with Sr-feldspar and Carich plagioclase, respectively. In the domains, approximately 3 nm large e-fringes can be seen (Fig.…”

Section: Lamellae and Local Domainssupporting

confidence: 85%

“…The lamellae merge without defects or structure stresses be-cause there is only a slight difference in cell parameters in the plagioclase series of 0.1 %, and the γ angle differs by only 0.4 % (Hoshi et al, 1996). This has been observed by a minor splitting of Kikuchi lines (Nissen, 1971;Nissen et al, 1973;Hoshi et al, 1996).…”

Section: Labradorescencementioning

confidence: 96%

“…This marks the position of the Bøggild miscibility gap in which lamellar intergrowths of e1 and e2 are formed. Various endmember compositions of the Bøggild intergrowth are given in the literature with An 40 -An 50 (Hoshi et al, 1996;Putnis, 2001), An 35-40 -An 50-55 (Nissen, 1971), An 44-45 (lower limit) (Jin and Xu, 2017a), An 47 -An 53 (Smith and Brown, 1988), An 51 -An 50 (Bøggild, 1924) and An 45 -An 65 (Okrusch and Matthes, 2013).…”

Section: E-plagioclasementioning

confidence: 99%

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The hierarchical internal structure of labradorite

Götz

Kleebe²,

Kolb³

2022

Eur. J. Mineral.

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Abstract. The different structural features of labradorite and its incommensurate atomic structure have long been in the eye of science. In this transmission electron microscopy (TEM) study, all of the structural properties of labradorite could be investigated on a single crystal with an anorthite–albite–orthoclase composition of An53.4Ab41.5Or5.1. The various properties of labradorite could thus be visualized and connected to form a hierarchical structure. Both albite and pericline twins occur in the labradorite. The size of alternating Ca-rich and Ca-poor lamellae could be measured and linked to the composition and the color of labradorescence. Furthermore, a modulation vector of 0.0580(15)a* + 0.0453(33)b* − 0.1888(28)c* with a period of 3.23 nm was determined. The results indicate an eα labradorite structure, which was achieved by forming Ca-rich and Ca-poor lamellae. The average structure and subsequently the incommensurate crystal structure were solved with a three-dimensional electron diffraction (3DED) data set acquired with automated diffraction tomography (ADT) from a single lamella. The results are in good agreement with the structure solved by X-ray diffraction and demonstrate that 3DED–ADT is suitable for solving even incommensurate structures.

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Section: Lamellae and Local Domainssupporting

confidence: 85%

Section: Labradorescencementioning

confidence: 96%

Section: E-plagioclasementioning

confidence: 99%

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The hierarchical internal structure of labradorite

Götz

Kleebe²,

Kolb³

2022

Eur. J. Mineral.

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“…Q od ( I

\overset{1}{true}

, P

\overset{1}{true}

) defines the state of Al/Si order relative to completely ordered anorthite as (≪Al–O≫ − ≪Si–O≫)/0.135 . Composition and structural state were taken from Carpenter et al ., except for An 46 Ab 64 and An 99 Ab 1 …”

Section: Methodsmentioning

confidence: 99%

Plagioclase composition by Raman spectroscopy

Bersani

Aliatis

Tribaudino

et al. 2018

J Raman Spectroscopy

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Plagioclase undergoes complex exsolution and ordering and phase transition processes during their evolution in nature, and this has hindered attempts to define simple trends relating the major peaks of their Raman spectra with composition. Here, the peak position and linewidth of major Raman features have been calibrated for a set of 20 plagioclases, spanning from albite to anorthite in composition, with symmetry and ordering states that were already well characterized. Point group symmetry is the most important factor determining the Raman peak behaviour with composition, though C true1¯, I true1¯, and P true1¯ plagioclases show different trends for the position of the main peak νa at ~500 cm−1. Using a simplifying approach, which merges the effect of Al–Si ordering and incommensurate modulations, a method has been developed to estimate the plagioclase composition from calibration of a few determinative Raman peaks. This makes use of the wavenumber difference Δab between the most intense peaks νa and νb around 500 cm−1, the linewidth Гa of the strongest νa peak, and the wavenumber difference Δcb between νc and νb peaks, where νc is a Raman feature at ~560–580 cm−1. The calibration was completed from data sets composed of spectra from metamorphic to pegmatitic plagioclase. The results were then tested against a further data set, mostly made by volcanic plagioclase. In most samples, the difference between electron micro probe analysis (EMPA) and Raman compositions is less than 5%. Higher residuals (beyond 10%) are observed for intermediate plagioclase, suggesting that some differences in Δab exist between volcanic and metamorphic plagioclase of intermediate compositions. The Raman compositional results for a plagioclase from Marsili submarine volcano agree with composition and zoning found from the analysis by laser ablation.

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“…Similarly, as demonstrated by the An 78 data, changes in the bulk moduli of the intermediate plagioclases with An content >50% are small because the best ordered samples still retain considerable compositionally induced disorder. The elasticity of plagioclases of An 85 ÀAn 100 is complicated by the influence of the P1 to I1 transition, their resulting complex modulated microstructures (Nemeth et al, 2007), and the interplay between Al/Si ordering and the transition . The latter probably explains why the softening associated with Al/Si disorder in anorthite appears stronger than in albite but this only occurs in anorthites annealed experimentally near the melting point and is probably not relevant for natural anorthites which exhibit very high degrees of Al/Si order (e.g.…”

Section: Discussionmentioning

confidence: 99%

The effect of Al/Si disorder on the bulk moduli of plagioclase feldspars

2010

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The volumes of a disordered An20 (Qod = 0.15), a disordered An78 (Qod = 0.55) and an ordered An78 (Qod = 0.81) were determined up to 9.569(10) GPa, 8.693(5) GPa and 9.765(10) GPa, respectively, using single-crystal X-ray diffraction. The volume variations with pressure for these samples are described with 4th-order Birch Murnaghan equations of state with V0 = 669.88(7) Å3, K0 = 59.7(7) GPa. K′ = 5.7(5), K″ = −0.8(2) GPa−1 for disordered An20, V0 = 1340.48(10) Å3, K0 = 77.6(5) GPa, K0′ = 4.0(3), K″ = -0.59(9) GPa−1 for disordered An78 and V0 = 1339.62(6) A3, K0 = 77.4(6) GPa, K′ = 4.2(4), and K″ = −0.7(1) GPa−1 for ordered An78. Along with data from previous studies (An0 ordered, An0 disordered and An2o ordered), the volumes for the disordered samples were found to be up to ∼0.3% larger than the ordered samples of the same composition. The disordered samples are softer than the ordered samples of the same composition by 4(1)% for An0, 2.5(9)% for An20 and essentially zero for An78. The relationship between volume increase, density decrease, and decreasing bulk modulus with increasing disorder is in accordance with Birch's Law.

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TEM investigation of Ca-rich plagioclase: Structural fluctuations related to the IFormula-PFormula phase transition

Cited by 10 publications

References 21 publications

The hierarchical internal structure of labradorite

The hierarchical internal structure of labradorite

Plagioclase composition by Raman spectroscopy

The effect of Al/Si disorder on the bulk moduli of plagioclase feldspars

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