The P21/m ↔ C2/m phase transition in amphiboles: new data on synthetic Na(NaMg)Mg5Si8O22F2 and the role of differential polyhedral expansion

Cámara, Fernando; Oberti, Roberta; Casati, Nicola

doi:10.1524/zkri.2008.0012

Cited by 9 publications

(3 citation statements)

References 25 publications

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“…It is now well-established that clinopyroxene undergoes a rapid reversible and nonquenchable displacive phase transition in which the P2 1 /c polymorph transforms to a high-T C2/c form ("HT-C2/c") at room-P and a high-P C2/c form ("HP-C2/c") at or below room-T Cámara et al (2007); 12 Iezzi et al (2007) kanoite). The two C-centered polymorphs have very different structures: the HT-C2/c phase has a fully-extended chain of tetrahedra, whereas the HP-C2/c phase has a strongly kinked chain.…”

Section: Comparisons With the P2 1 /C ↔ C2/c Transitions In Pyroxenesmentioning

confidence: 99%

Non-Ambient in situ Studies of Amphiboles

Welch

Cámara

Ventura

et al. 2007

Reviews in Mineralogy and Geochemistry

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Section: Comparisons With the P2 1 /C ↔ C2/c Transitions In Pyroxenesmentioning

confidence: 99%

Non-Ambient in situ Studies of Amphiboles

Welch

Cámara

Ventura

et al. 2007

Reviews in Mineralogy and Geochemistry

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“…A series of in-situ experiments have been performed on the low and high thermal behavior of amphiboles, on the basis of several experimental techniques (e.g., Sueno et al 1978;Cameron et al 1983;Cámara et al 2003Cámara et al , 2007Iezzi et al 2005a;Jenkins and Corona 2006), reviewed by Welch et al (2007). Some more recent studies are, e.g., those of Tribaudino et al (2008), Welch et al (2008) and Iezzi et al (2011) on richterite, Welch et al (2011b) on anthophyllite and Zema et al (2012) on gedrite.…”

Section: Introductionmentioning

confidence: 99%

Pargasite at high pressure and temperature

et al. 2017

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The P-T phase stability field, the thermo-elastic behavior and the P-induced compression mechanisms at the atomic scale of pargasite crystals from the "phlogopite peridotite unit" of the Finero mafic-ultamafic complex (Ivrea-Verbano Formation, Italy) have been investigated by a series of in-situ experiments: a) at high pressure (up to 20.1 GPa), by single-crystal synchrotron Xray diffraction with a diamond anvil cell, b) at high temperature (up to 823 K), by powder synchrotron X-ray diffraction using a hot air blower device, and c) at simultaneous HP-HT conditions, by single-crystal synchrotron X-ray diffraction with a resistive-heated diamond anvil cell (Pmax = 16.5 GPa, Tmax = 1200 K). No phase transition has been observed within the P-T range investigated. At ambient T, the refined compressional parameters, calculated by fitting a secondorder Birch-Murnaghan Equation of State (BM-EoS), are: V0 = 915.2(8) Å 3 and KP0,T0 = 95(2) GPa (P0,T0 = 0.0121(2) GPa -1 ) for the unit cell volume; a0= 9.909(4) Å and K(a)P0,T0 = 76(2) GPa for the a-axis; b0 = 18.066(7) Å and K(b)P0,T0 = 111(2) GPa for the b-axis; c0 = 5.299(5) Å and K(c)P0,T0 = 122(12) GPa for the c-axis [K(c)P0,T0 ~ K(b)P0,T0 > K(a)P0,T0]. The high-pressure structure refinements (at ambient T) show a moderate contraction of the TO4 double chain and a decrease of its bending in response to the hydrostatic compression, along with a pronounced compressibility of the A-and M(4)-polyhedra [KP0,T0(A) = 38(2) GPa, KP0,T0(M4) = 79(5) GPa] if compared to the M(1)-, M(2)-, M(3)-octahedra [KP0,T0(M1,2,3) ≤ 120 GPa] and to the rigid tetrahedra [KP0,T0(T1,T2)~ 300 GPa]. The thermal behavior, at ambient pressure up to 823 K, was modelled with Berman's formalism, which gives: V0 = 909.1(2) Å 3 , α0 = 2.7(2)•10 -5 K -1 and α1= 1.4(6)•10 -9 K -2 [with α0(a) = 0.47(6)•10 -5 K -1 , α0(b) = 1.07(4)•10 -5 K -1 , and α0(c) = 0.97(7)•10 -5 K -1 ]. The petrological implications of the experimental findings of this study are discussed.

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“…At room temperature, the P2 1 /m phase occurs in the Mg-richer portion of the cummingtonite-grunerite join (Hirshmann et al 1994;Yang and Prewitt 2000;Boffa-Ballaran et al 2004). Recent works have also shown that synthetic "magnesiorichterite" [MRIC: Na(NaMg)Mg 5 Si 8 O 22 (OH) 2 ] and amphiboles along the join Na(NaMg)Mg 5 Si 8 O 22 (OH) 2 -Na(LiMg)Mg 5 Si 8 O 22 (OH) 2 have P2 1 /m symmetry (Iezzi et al 2004(Iezzi et al , 2006aCámara et al 2008).…”

Section: Introductionmentioning

confidence: 99%

The high-temperature P21/m -> C2/m phase transitions in synthetic amphiboles along the richterite-(BMg)-richterite join

Iezzi

Tribaudino

Ventura

et al. 2011

American Mineralogist

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The thermal behavior of three amphiboles along the join "Mg-richterite" [MRIC: A Na B (NaMg) C Mg 5 T Si 8 O 22 W (OH) 2 ]-richterite [RIC: A Na B (NaCa) C Mg 5 T Si 8 O 22 W (OH) 2 ] was investigated by in situ synchrotron radiation powder diffraction between 90 and 873 K. The studied samples have Bsite compositions Na 1 Mg 1 (sample RN1), Na 0.97 Mg 0.8 Ca 0.24 (sample RN2), and Na 0.97 Mg 0.58 Ca 0.45 (sample RN6).The evolution of cell parameters as a function of T shows a discontinuity in the two Mg-richer samples (RN1 and RN2), which is interpreted as evidence of a P2 1 /m → C2/m phase transition, whereas the Ca-richer sample (RN6) shows no evidence of a phase transition. The transition in samples RN1 and RN2 follows a different thermodynamic behavior, being tricritical in end-member "Mg-richterite" (RN1) and second order in the B Ca-bearing amphibole RN2. A thermodynamic analysis done according to the Landau formalism and allowing for order parameter saturation, gives T c = 462(3) and 378(1) K, and saturation temperature θ s =116(21) and 141(7) for RN1 and RN2, respectively.Comparison with data from literature shows that the thermal strain of C-centered amphiboles with constant A-, C-, T-, and W-site occupancy equal to Na, Mg 5 , Si 8 , and (OH) 2 , respectively, and a B-site occupied by variable amounts of Li, Na, Mg, and/or Ca, mainly expands about 70° from c toward the a cell-edge onto the 010 plane. Conversely, the spontaneous strain accompanying the thermal transition shows that the maximum expansion is oriented about 25° from c and is coupled with a contraction close to the a cell direction. On the other side, transition induced by solid solution at room-T follows an almost opposite deformation pattern.The present data confirm the hypothesis of a first-order character of the transition induced by the increase of the B-site dimension for increasing B Ca contents, similarly to the closely related P2 1 /c → C2/c transition in pyroxenes.

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The P2₁/m ↔ C2/m phase transition in amphiboles: new data on synthetic Na(NaMg)Mg₅Si₈O₂₂F₂ and the role of differential polyhedral expansion

Cited by 9 publications

References 25 publications

Non-Ambient in situ Studies of Amphiboles

Non-Ambient in situ Studies of Amphiboles

Pargasite at high pressure and temperature

The high-temperature P21/m -> C2/m phase transitions in synthetic amphiboles along the richterite-(BMg)-richterite join

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