7T wollastonite from Fuka, Okayama Prefecture

Henmi, Chiyoko; Kusachi, Isao; Kawahara, Akira; Henmi, Kitinosuke

doi:10.2465/minerj.9.169

Cited by 14 publications

(13 citation statements)

References 9 publications

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“…Depending on the packing arrangement of the SiO 3 chains, a series of polytypes of wollastonite are realized (Wenk 1969;Henmi et al 1978Henmi et al , 1983. A selected area electron diffraction (SAED) pattern of this wollastonite (Fig.…”

Section: Polytypes Of Wollastonitementioning

confidence: 98%

Clinopyroxene exsolution in wollastonite from Namaqualand granulite, South Africa

Seto

Ohi

Shimobayashi

et al. 2006

American Mineralogist

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Chemical and crystallographic properties of clinopyroxene exsolution in wollastonite are described from metamorphosed calc-silicate granulite, Namaqualand, South Africa. The wollastonite is Ca 1.96 Fe 0.01 Al 0.01 Si 2.01 O 6 belonging to space group P2 1 /a (2M polytype) and the clinopyroxene is Ca 0.99 Mg 0.75-0.80 Fe 0.17-0.21 Na 0.02 Al 0.03 Si 1.99-2.00 O 6 belonging to C2/c. An electron backscattered diffraction investigation suggests that the clinopyroxene lamellae elongated along [1 -1 -1] lie on (120) and (100) of the wollastonite-2M, and [11 -0] of both lamellae are parallel to [001] of the wollastonite-2M. The formation of the exsolution probably results from the relatively high peak metamorphic temperature (800-860ºC) of the Namaqualand granulite and its slow cooling rate.

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Section: Polytypes Of Wollastonitementioning

confidence: 98%

Clinopyroxene exsolution in wollastonite from Namaqualand granulite, South Africa

Seto

Ohi

Shimobayashi

et al. 2006

American Mineralogist

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“…Two polytypes of wollastonite are common, consisting of a one-layer repeat structure and one with a two-layer repeat, while longer period polytypes have also been reported (Henmi et al, 1978(Henmi et al, , 1983. Wollastonite, CaSi0 3 , exhibits polytypism based upon the stacking of (100) layers of structure which may be stacked by one of two stacking vectors; a zero displacement, or one of 1/2[010] which is one-half of the chain repeat distance along the silicate chains.…”

Section: Compositional Restrictionsmentioning

confidence: 99%

Polytypes and polytypism

Angel¹

1986

Zeitschrift Für Kristallographie - Crystalline Materials

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The definition of polytypism recommended by the IMA/IUCr joint committee on nomenclature is reviewed in the light of the structural variation observed in mineral and alloy systems. As a result of this review it is concluded that previous definitions of polytypism are too restrictive -to be practical, and a definition which emphasises the structural basis of polytypism is proposed: "Polytypism arises from the different modes of stacking of one or more structurally compatible modules."The various types of structural variation included under this definition are described using as examples minerals, ceramics, and alloys.

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“…These are/TI'G) and (TYITG) (Henmi et al, 1983), both of which appear in the phase diagram at elevated temperatures with stability fields of significant size, and iTI'GTGTG) (Henmi, Kusachi, Kawahara & Henmi, 1978) which maps onto the ANNNI spin sequence (152). This seven-layer polytype is thus one of the structures which is stable on the multiphase boundary between (TG) and /TITG) in the ground state, but does not appear in the low-temperature region of the phase diagram shown in Figs.…”

Section: Wollastonitementioning

confidence: 99%

“…However, in the ANNNI model i152) does have a restricted stability field at higher temperatures where significant disorder is present within the layers, so/TI'GTGTG) will have a similar stability field in the phase diagram of the wollastonite model. Whether its occurrence in the material examined by Henmi et al (1978) is due to growth within this restricted stability field, or to metastable growth under other conditions cannot be determined. Metastability is always a consideration in these systems because the free-energy differences between polytypes are so small.…”

Section: Wollastonitementioning

confidence: 99%

The energetics of polytypic structures: further applications of the ANNNI model

Angel¹,

Price²,

Yeomans³

1985

Acta Crystallogr Sect B

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The stability of long-period polytype stacking sequences can be shown to be dependent upon the energy contribution from interactions between the constituent modules (layers). Previous work has concentrated upon interactions between nearest and nextnearest (i.e. first and second) neighbour layers. It is shown that in some polytype systems, such as wollastonite, the equivalence of certain pairs of stacking sequences places constraints upon the allowed interactions between the modules. A mapping between these polytypic systems and a simple spin model, the Axial Next-Nearest-Neighbour Ising (ANNNI) model is developed in order to derive a theoretical phase diagram for these polytypes. The predictions of this phase diagram regarding the relative stability of polytype stacking sequences are shown to compare favourably with observations reported for natural mineral systems.

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7T wollastonite from Fuka, Okayama Prefecture

Cited by 14 publications

References 9 publications

Clinopyroxene exsolution in wollastonite from Namaqualand granulite, South Africa

Clinopyroxene exsolution in wollastonite from Namaqualand granulite, South Africa

Polytypes and polytypism

The energetics of polytypic structures: further applications of the ANNNI model

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