Abstract:The chemical composition, [Mg0.015 (2),Al1.20 (2),Si2.99 (1),Ca3.00 (2),Ti0.027 (3),Mn0.017 (3), Fe0.75 (3)]O12 (magnesium aluminium silicon calcium titanium manganese iron dodecaoxide), of a natural garnet collected at Diamantina, Minas Gerais, Brazil was determined by electron microprobe analysis. The structure refinement from X‐ray powder data is insensitive to the small amounts of Ti, Mn and Mg. The determined cation distribution using the Rietveld method is {Ca32+}[Al1.338 (8)3+,Fe0.662 (8)3+](Si34+)O12… Show more
“…Therefore, disagreements between the real and calculated Al sofs should be also most probably treated as a consequence of some polyhedral distortions and crystal disordering and their longer 〈 Y –O〉 distances, as well. Nevertheless, this is not so unusual phenomenon because more or less discrepancies between SCXRD, XRPD, and HRPXRD methods with chemical and EMPA compositions are already observed elsewhere (see Gali, 1984; Resende and Fernandes, 2005; Antao and Klincker, 2013).…”
Section: Resultssupporting
confidence: 51%
“…Also, Diamantina disordering is of different kind than Meka Presedla (previously explained within discussion about criterion (II); Supplementary Material 8) because it has longer 〈 Y –O〉 and 〈 X ′–O〉 but shorter 〈 X ″–O〉 and 〈 X –O〉 distances than it should be expected from its chemical composition. As shown by Resende and Fernandes (2005), in this grandite the arrangement of the cations around the O atom is best described as a highly distorted tetrahedral, due that the O atom is displaced by 0.267(7) Å from the plane defined by Ca 2+ , Si 4+ , and Y = Al 3+ /Fe 3+ . Figure 9.(Color online) Comparison of the Fe 3+ and Al 3+ variations over the octahedral sites by the octahedral average 〈 Y –O〉 distances for the Meka Presedla rhombohedral (blue) and orthorhombic Fddd (orange) space groups, Diamantina cubic space group (green), and Munam triclinic space group (red) grandites.…”
Section: Resultsmentioning
confidence: 57%
“…Two grandite samples, very similar to our sample by their chemical composition, were found in the available literature data. These are Grs 60 Adr 38 –Grs 67 Adr 33 from Diamantina, Brazil (XRPD; cubic space group; a 0 = 11.922(1) Å; Resende and Fernandes, 2005), and Grs 67 Adr 33 from Munam, North Korea (SCXRD; triclinic space group; a 0 = 11.920(2) Å; b 0 = 11.922(2) Å; c 0 = 11.920(2) Å; 〈 a 0 〉 = 11.921(2) Å; α 0 = 90.03(1)°; β 0 = 90.12(1)°; γ 0 = 89.98(1)°; Al sofs 51–85 at.% over the eight Y sites; Takéuchi et al ., 1982). Also, these have very similar unit cell dimensions with ours ( space group: a 0 = 11.9191(7) Å; Table I; and space group: 〈 a 0 〉 = 11.919(1) Å; Supplementary Material 4).…”
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.
“…Therefore, disagreements between the real and calculated Al sofs should be also most probably treated as a consequence of some polyhedral distortions and crystal disordering and their longer 〈 Y –O〉 distances, as well. Nevertheless, this is not so unusual phenomenon because more or less discrepancies between SCXRD, XRPD, and HRPXRD methods with chemical and EMPA compositions are already observed elsewhere (see Gali, 1984; Resende and Fernandes, 2005; Antao and Klincker, 2013).…”
Section: Resultssupporting
confidence: 51%
“…Also, Diamantina disordering is of different kind than Meka Presedla (previously explained within discussion about criterion (II); Supplementary Material 8) because it has longer 〈 Y –O〉 and 〈 X ′–O〉 but shorter 〈 X ″–O〉 and 〈 X –O〉 distances than it should be expected from its chemical composition. As shown by Resende and Fernandes (2005), in this grandite the arrangement of the cations around the O atom is best described as a highly distorted tetrahedral, due that the O atom is displaced by 0.267(7) Å from the plane defined by Ca 2+ , Si 4+ , and Y = Al 3+ /Fe 3+ . Figure 9.(Color online) Comparison of the Fe 3+ and Al 3+ variations over the octahedral sites by the octahedral average 〈 Y –O〉 distances for the Meka Presedla rhombohedral (blue) and orthorhombic Fddd (orange) space groups, Diamantina cubic space group (green), and Munam triclinic space group (red) grandites.…”
Section: Resultsmentioning
confidence: 57%
“…Two grandite samples, very similar to our sample by their chemical composition, were found in the available literature data. These are Grs 60 Adr 38 –Grs 67 Adr 33 from Diamantina, Brazil (XRPD; cubic space group; a 0 = 11.922(1) Å; Resende and Fernandes, 2005), and Grs 67 Adr 33 from Munam, North Korea (SCXRD; triclinic space group; a 0 = 11.920(2) Å; b 0 = 11.922(2) Å; c 0 = 11.920(2) Å; 〈 a 0 〉 = 11.921(2) Å; α 0 = 90.03(1)°; β 0 = 90.12(1)°; γ 0 = 89.98(1)°; Al sofs 51–85 at.% over the eight Y sites; Takéuchi et al ., 1982). Also, these have very similar unit cell dimensions with ours ( space group: a 0 = 11.9191(7) Å; Table I; and space group: 〈 a 0 〉 = 11.919(1) Å; Supplementary Material 4).…”
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.
“…As pre vi ously shown by Tanèiae et al (2020), there are only two fer ric grossular sam ples found in the avail able lit er a ture, which have very sim i lar chem i cal com po si tions to our sam ple. These are Grs 60 Adr 38 -Grs 67 Adr 33 from Dia man tina, Brazil (cubic Ia63d space group, Resende and Fernandes, 2005), and Grs 67 Adr 33 from Munam, North Ko rea (triclinic I61 space group, Takéuchi et al, 1982). How ever, these three fer ric grossular gar nets are ob vi ously struc tur ally very dif fer ent be tween each other, as all of them crys tal lize not only in dif fer ent space groups, but also in dif fer ent crys tal lo graphic sys tems.…”
Section: Polyhedral Distortions and Structural Disordering Between Th...mentioning
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 mean-square amplitudes of vibration of the oxygen atom are higher in a direction approximately perpendicular to the bond. In a Rietveld refinement, a natural garnet showed similar behavior (Resende and Fernandes, 2005).…”
A natural sodalite from the geological site Alkaline Complex of Floresta Azul, Bahia, Brazil, has been characterized by electron microprobe, infrared spectroscopy, and powder high-resolution X-ray diffraction techniques. The mineral is an aluminosilicate framework, formed by cages called sodalite unity. Although the sample is natural, the chemical analysis reveals that it is indeed the end member sodalite sensu strictu, Na 8 ͓Si 6 Al 6 O 24 ͔Cl 2 . Infrared spectroscopy shows Si, Al tetrahedral-oxygen stretching nonsymmetric mode, stretching symmetric mode, and bending modes. Indexing of the experimental X-ray diffraction pattern led to cubic space group P-43n, and unit-cell parameters: a = 8.8767͑7͒ Å, D x = 2.301 g cm −3 , and V = 699.46͑1͒ Å 3 . X-ray diffraction data are reported. Rietveld refinement was also performed, and the confidence factors are Rp= 0.079, Rwp= 0.118, and 2 = 2.19. The structure of the minerals of sodalite group holds four different tetrahedra: AlO 4 , ClNa 4 , Na͑ClO 3 ͒, and SiO 4 , with Al, Cl, Na, and Si located at the center of each tetrahedron.
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