Abstract:The cation ordering of the {110} c and {211} c growth sectors in birefringent garnet from Kayas, Mali was investigated by means of single-crystal X-ray diffraction (SC-XRD) 3d were observed, and crystal structure models for both the {110} c and {211} c sectors should have triclinic symmetry with the space group I 1. The unit-cell parameters of both growth sectors were a = 11.9739(13), b = 11.9742(14), c = 11.9737(13) Å, α = 90.001(9), β = 90.098(9) and γ = 90.014 (10)°for the {110} c sector; a = 11.952(6), b… Show more
“…their returning to the more "regular" positions after constraints were applied ( Supplementary Materials 8 and 13). Also, more or less declinations from the grossular-andradite join are visible at low symmetry grandite samples previously studied by Frank-Kamenetskaya et al (2007), Kobayashi et al (2013), and Nakamura et al (2016); whereas Wildner and Andrut (2001) described declinations from the grossular-uvarovite join of their studied low symmetry uvarovite samples. Shtukenberg et al (2005) found that the difference in sofs should be proportional to the value of angle β 0 in the I 1 space group.…”
Section: B Crystal Structure Refinementsmentioning
confidence: 76%
“…(2013), and Nakamura et al . (2016); whereas Wildner and Andrut (2001) described declinations from the grossular–uvarovite join of their studied low symmetry uvarovite samples. Figure 7.Variations of the Fe 3+ and Al 3+ over the octahedral sites in the , , and Fddd space groups, by average (a) 〈 Y –O〉 and (b) 〈O–O〉 distances.…”
Section: Resultsmentioning
confidence: 99%
“…A substantial number of previously observed grandites exhibit optical anisotropy, indicating five possible causes for this phenomenon, such as (1) twinning (Ingerson and Barksdale, 1943; Brown and Mason, 1994); (2) substitution of rare-earth elements (REE) for Ca (Blanc and Maisonneuve, 1973); (3) non-cubic distribution of OH − groups, due to hydro-garnet substitution (Aines and Rossman, 1984; Rossman and Aines, 1986; Allen and Buseck, 1988; Andrut et al ., 2002; Badar et al ., 2016); (4) residual strain from lattice mismatch at compositional, twin, or grain boundaries (Chase and Lefever, 1960; Lessing and Standish, 1973; Foord and Mills, 1978; Kitamura and Komatsu, 1978; McAloon and Hofmeister, 1993, 1995; Hofmeister et al ., 1998; Shtukenberg et al ., 2001; Antao, 2013a, 2013b; Antao and Klincker, 2013); and (5) ordering of Fe 3+ and Al 3+ over the octahedral sites (Takéuchi and Haga, 1976; Takéuchi et al ., 1982; Gali, 1983, 1984; Akizuki, 1984, 1989; Allen and Buseck, 1988; Hatch and Griffen, 1989; Kingma and Downs, 1989; Griffen et al ., 1992; Akizuki et al ., 1998; Shtukenberg et al ., 2001, 2002, 2005, 2006; Frank-Kamenetskaya et al ., 2007; Kobayashi et al ., 2013; Badar et al , 2016; Nakamura et al , 2016).…”
In this paper, grandite core with Grs64±1Adr36±1Sps2 composition was crystallographically studied. This core represents zone A of the macroscopically visible five A–E zones of the optically anisotropic Grs58–64Adr36–42Sps2 grandite. The applied procedure includes the detailed analysis of the powder diffraction patterns, and the Rietveld refinements of the crystal structures in a series of 18 space groups and two mixtures, which were followed by the comparative analysis of the R-values, site occupancy factors, and the bond lengths and angles. Synthesis of all of the presented results allows us to undoubtedly conclude that studied grandite is not cubic, neither as monophase nor as multiple phases in a mixture. Namely, it was established that structural dissymmetrization occurred and that it crystallized in the disordered rhombohedral $R\bar{3}c$ or orthorhombic Fddd space groups, whereby the first one is more probable. Beside the established lower symmetry of the studied grandite, which could be treated as the primary cause, the residual strain is also not excluded as the second possible cause for its slight optical anisotropy.
“…their returning to the more "regular" positions after constraints were applied ( Supplementary Materials 8 and 13). Also, more or less declinations from the grossular-andradite join are visible at low symmetry grandite samples previously studied by Frank-Kamenetskaya et al (2007), Kobayashi et al (2013), and Nakamura et al (2016); whereas Wildner and Andrut (2001) described declinations from the grossular-uvarovite join of their studied low symmetry uvarovite samples. Shtukenberg et al (2005) found that the difference in sofs should be proportional to the value of angle β 0 in the I 1 space group.…”
Section: B Crystal Structure Refinementsmentioning
confidence: 76%
“…(2013), and Nakamura et al . (2016); whereas Wildner and Andrut (2001) described declinations from the grossular–uvarovite join of their studied low symmetry uvarovite samples. Figure 7.Variations of the Fe 3+ and Al 3+ over the octahedral sites in the , , and Fddd space groups, by average (a) 〈 Y –O〉 and (b) 〈O–O〉 distances.…”
Section: Resultsmentioning
confidence: 99%
“…A substantial number of previously observed grandites exhibit optical anisotropy, indicating five possible causes for this phenomenon, such as (1) twinning (Ingerson and Barksdale, 1943; Brown and Mason, 1994); (2) substitution of rare-earth elements (REE) for Ca (Blanc and Maisonneuve, 1973); (3) non-cubic distribution of OH − groups, due to hydro-garnet substitution (Aines and Rossman, 1984; Rossman and Aines, 1986; Allen and Buseck, 1988; Andrut et al ., 2002; Badar et al ., 2016); (4) residual strain from lattice mismatch at compositional, twin, or grain boundaries (Chase and Lefever, 1960; Lessing and Standish, 1973; Foord and Mills, 1978; Kitamura and Komatsu, 1978; McAloon and Hofmeister, 1993, 1995; Hofmeister et al ., 1998; Shtukenberg et al ., 2001; Antao, 2013a, 2013b; Antao and Klincker, 2013); and (5) ordering of Fe 3+ and Al 3+ over the octahedral sites (Takéuchi and Haga, 1976; Takéuchi et al ., 1982; Gali, 1983, 1984; Akizuki, 1984, 1989; Allen and Buseck, 1988; Hatch and Griffen, 1989; Kingma and Downs, 1989; Griffen et al ., 1992; Akizuki et al ., 1998; Shtukenberg et al ., 2001, 2002, 2005, 2006; Frank-Kamenetskaya et al ., 2007; Kobayashi et al ., 2013; Badar et al , 2016; Nakamura et al , 2016).…”
In this paper, grandite core with Grs64±1Adr36±1Sps2 composition was crystallographically studied. This core represents zone A of the macroscopically visible five A–E zones of the optically anisotropic Grs58–64Adr36–42Sps2 grandite. The applied procedure includes the detailed analysis of the powder diffraction patterns, and the Rietveld refinements of the crystal structures in a series of 18 space groups and two mixtures, which were followed by the comparative analysis of the R-values, site occupancy factors, and the bond lengths and angles. Synthesis of all of the presented results allows us to undoubtedly conclude that studied grandite is not cubic, neither as monophase nor as multiple phases in a mixture. Namely, it was established that structural dissymmetrization occurred and that it crystallized in the disordered rhombohedral $R\bar{3}c$ or orthorhombic Fddd space groups, whereby the first one is more probable. Beside the established lower symmetry of the studied grandite, which could be treated as the primary cause, the residual strain is also not excluded as the second possible cause for its slight optical anisotropy.
“…Spe cies of the grossular-an dra dite {Ca 3 }[Al,Fe 3+ ] 2 (Si 3 )O 12 solid-so lu tion bi nary se ries, oc cur ring in a va ri ety of geo log i cal en vi ron ments, are known to ap pear in the form of zoned crystals (Deer et al, 2013;Tanèiae et al, 2012a and ref er ences therein). A sub stan tial num ber of pre vi ously-ob served grossular-an dra dite gar nets ex hibit op ti cal ani so tropy and non-cu bic low sym me try in var i ous space groups, such as: I61 (Takéuchi et al, 1982;Allen and Buseck, 1988;Kingma and Downs, 1989;Frank-Kamenetskaya et al, 2007;Kobayashi et al, 2013;and Nakamura et al, 2016); Fddd (Takéuchi et al, 1982;Gali, 1984;Frank-Kamenetskaya et al, 2007;Badar et al, 2016); Fddd or C2/c (Hirai and Nakazawa, 1986) and R63c or Fddd (Tanèiae et al, 2020).…”
As so ci ate Editor: Tomasz Bajda Four mac ro scop i cally vis i ble B-E (rim) zones, within a large nat u ral fer ric grossular gar net of Grs 58-64 Adr 36-42 Sps 2 com po sition, are de scribed by means of Rietveld re fine ments of the crys tal struc tures in a se ries of six space groups, fol lowed by com par a tive anal y sis of the R-val ues, site oc cu pancy fac tors, and bond lengths and an gles. The gar net crys tal lized in the rhombohedral R63c space group. Var i ous poly he dral dis tor tions and struc tural or der-dis or der vari a tions be tween the zones stud ied are also de scribed and dis cussed. The rhombohedral sym me try of the fer ric grossular gar net ana lysed can be regarded as pri mary, re sid ual strain be ing a sec ond ary cause for its slight op ti cal ani so tropy.
“…The crystal structures of birefringent ugrandite were reported as orthorhombic structure with the space group Fddd or triclinic structure with the space group I 1 (e.g. Takéuchi et al, 1982;Allen and Buseck, 1988;Wildner and Andrut, 2001;Frank-Kamenetskaya et al, 2007;Kobayashi et al, 2013;Nakamura et al, 2016). Kingma and Downs (1989) examined the crystal structure of iridescent andradite from a skarn deposit in the Sonoma Range, Nevada, USA.…”
The crystal structure of iridescent garnet from Tenkawa village, Nara prefecture, Japan was investigated by means of Single-crystal X-ray diffraction method. The garnet crystal is composed of {110} c and {211} c growth sectors and shows birefringence under the crossed polarizer. The BSE image of the cross section shows very fine lamellae texture consisting of andradite-rich and grossular-rich layers. The average chemical composition was determined as Ca 3.01 (Fe 1.93 Al 0.09 ) Σ2.02 Si 2.99 O 12 . The unit-cell parameters were obtained as follows; a = 12.0540(17), b = 12.0580(13), c = 12.0612(13) Å, α = 89.986(9), β = 89.994(10) and γ = 89.994 (10)°. Some reflections which violate the extinction rule for the space group Ia 3d were observed and indicated that all glide planes are absent. Triclinic symmetry with the space group I 1 should be suitable for the structure refinement. The refinement with a I 1 model was convergent with R1 = 3.19%. The Fe 3+ occupancies of the Y11, Y12, Y13, Y14, Y 21, Y22, Y 23, and Y 24 were determined as 86.9(6), 96.1(6), 90.9(6), 98.0(6), 95.1(6), 91.3(6), 93.7(6), and 99.6(6)%, respectively. The Fe 3+ occupancy of the Y11 site is relatively lower, and that of the Y 24 site is higher. The iridescent garnet from Tenkawa shows very fine lamellae texture consisted of Fe-rich and Al-rich layers, therefore, the refined crystal structure of the Tenkawa garnet should be a superimposed structure of these chemically distinct layers. The Fe-rich layer have almost pure andradite composition, so cation ordering in the Fe-rich layer is negligible. The Al-rich layer should have more obvious ordered cation distribution than the Ferich layer. The ordered cation distribution in the Al-rich layer should mainly contribute the cation ordering in the refined crystal structure of the Tenkawa garnet.
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