Abstract:ABSTRACT. A Ca-poor rhodonite (CaO 1.31 wt.%), found in a quartz vein cutting manganese ore bodies, north of the Xanthi plutonic complex (northeastern Greece) was studied. Microprobe analyses with optical and physical properties are given. The cell dimensions, obtained by least squares calculation from direct 0 value measurements on a Philips PW1100 single-crystal diffractometer are a = 7.626, b = 11.844, c = 6.702 A, ~, = 92.44 ~ = 94.28 ~ ~ = 105.70 ~ v= 579.89A 3, z = 10, and space group PI. R HOD O s I T E… Show more
“…These studies include Peacor and Niizeki (1963), Momoi (1964), Ito (1972), Ohashi and Finger (1975), Viswanathan and Harneit (1986), Pinckney and Burnham (1988), and Livi and Veblen (1992). Sapountzis and Christofi des (1982) described a Ca-poor rhodonite, and Peacor et al (1978) refi ned the crystal structure of an Mg-rich rhodonite. Dickson (1975) presented Mössbauer spectra of rhodonite.…”
Rhodonite (ideally MnSiO 3 ) is a triclinic pyroxenoid that typically contains signifi cant concentrations of Ca, Fe, and Mg. A variety called fowlerite contains concentrations of Zn up to 10 wt% and has been found only at Franklin, New Jersey. Data from electron microprobe analyses, single-crystal X-ray structure refi nements, and preliminary Mössbauer spectra suggest marked differences in the crystal chemistry of rhodonite and fowlerite. Cations in Zn-poor rhodonites and in fowlerites exhibit distinct substitutional trends. Substitution of Zn in fowlerite occurs entirely at M4, and Ca displays a stronger preference for M5 in fowlerite than in Zn-poor rhodonite. Further, the distinctive compositional variations in fowlerite lead to strongly mutually correlated lattice parameter variations distinct from those in Zn-poor rhodonite. Mean M-O distances in fowlerite, with the exception of , are strongly correlated with all unit-cell edges. For Zn-poor rhodonites, neither nor are signifi cantly correlated with cell edges, and the mean bond lengths for M1, M3, and M5 are correlated strongly with only a and b.The most striking distinctions between fowlerite and typical rhodonite occur in the geometrical details of M4 and M5. Distortion in the M4 site of magnesian rhodonite, typical Mn-rich rhodonite, and fowlerite increases with both increasing electron population and mean electronegativity. The M4 site assumes increasing amounts of tetrahedral character with increasing electron density (i.e., increasing Zn concentration). As M4 becomes more Zn-rich, tetrahedral, and covalent in character, M5 becomes more Ca-rich, less distorted, and more ionic in character. This suggests that "pure" fowlerite (nominally Ca 0.2 Zn 0.2 Mn 0.6 O 3 , or CaZnMn 3 O 15 ) may contain an unequivocally four-coordinated M4 site occupied solely by Zn, and with Ca largely restricted to M5.
“…These studies include Peacor and Niizeki (1963), Momoi (1964), Ito (1972), Ohashi and Finger (1975), Viswanathan and Harneit (1986), Pinckney and Burnham (1988), and Livi and Veblen (1992). Sapountzis and Christofi des (1982) described a Ca-poor rhodonite, and Peacor et al (1978) refi ned the crystal structure of an Mg-rich rhodonite. Dickson (1975) presented Mössbauer spectra of rhodonite.…”
Rhodonite (ideally MnSiO 3 ) is a triclinic pyroxenoid that typically contains signifi cant concentrations of Ca, Fe, and Mg. A variety called fowlerite contains concentrations of Zn up to 10 wt% and has been found only at Franklin, New Jersey. Data from electron microprobe analyses, single-crystal X-ray structure refi nements, and preliminary Mössbauer spectra suggest marked differences in the crystal chemistry of rhodonite and fowlerite. Cations in Zn-poor rhodonites and in fowlerites exhibit distinct substitutional trends. Substitution of Zn in fowlerite occurs entirely at M4, and Ca displays a stronger preference for M5 in fowlerite than in Zn-poor rhodonite. Further, the distinctive compositional variations in fowlerite lead to strongly mutually correlated lattice parameter variations distinct from those in Zn-poor rhodonite. Mean M-O distances in fowlerite, with the exception of , are strongly correlated with all unit-cell edges. For Zn-poor rhodonites, neither nor are signifi cantly correlated with cell edges, and the mean bond lengths for M1, M3, and M5 are correlated strongly with only a and b.The most striking distinctions between fowlerite and typical rhodonite occur in the geometrical details of M4 and M5. Distortion in the M4 site of magnesian rhodonite, typical Mn-rich rhodonite, and fowlerite increases with both increasing electron population and mean electronegativity. The M4 site assumes increasing amounts of tetrahedral character with increasing electron density (i.e., increasing Zn concentration). As M4 becomes more Zn-rich, tetrahedral, and covalent in character, M5 becomes more Ca-rich, less distorted, and more ionic in character. This suggests that "pure" fowlerite (nominally Ca 0.2 Zn 0.2 Mn 0.6 O 3 , or CaZnMn 3 O 15 ) may contain an unequivocally four-coordinated M4 site occupied solely by Zn, and with Ca largely restricted to M5.
“…Fig. 5.Ratios of the major metal cations in minerals of the rhodonite group ( a ) and pyroxmangite–pyroxferroite series ( b ), based on literature (Sundius, 1931; Hietanen, 1938; Peacor and Niizeki, 1963; Momoi, 1964; Burnham, 1971; Ohashi and Finger, 1975; Peacor et al , 1978; Sapountzis and Christofides, 1982; Pinckney and Burnham, 1988; Nelson and Griffen, 2005; Shchipalkina et al , 2017; Brusnitsyn, 2000, 2013; 2015; Shchipalkina et al , 2016; and reference therein) and our data. In ( a ) samples with determined crystal structures are marked by filled circles: blue – rhodonite; light purple – vittinkiite; deep purple – synthetic analogue of the end-member vittinkiite; red – ferrorhodonite; green – Zn-rich variety of rhodonite (‘fowlerite’); and grey – Mg-enriched variety of rhodonite.…”
Section: Identification Of Pyroxenoids With the Idealised Formula Mnsio3mentioning
confidence: 99%
“…This rhodonite-type mineral with a low Ca content has been known for a long time, however, it is much rarer than rhodonite sensu stricto , the idealised end-member formula of which is CaMn 4 [Si 5 O 15 ]. Such a Ca-poor rhodonite-group mineral has been reported undeniably from two localities in Finland, namely Vittinge (Sundius, 1931) and Simsiö (Hietanen, 1938), the Taguchi manganese deposit in Aichi Prefecture, Japan (Momoi, 1964), the Xanthi area in Greece (Sapountzis and Christofides, 1982), and the Malosedel'nikovskoe, Kurganovskoe, Kozhaevskoe and Faizulinskoe manganese and rhodonite deposits in the Urals, Russia (Brusnitsyn, 2013). It is noteworthy that, based on the chemical data on Uralian rhodonite, Brusnitsyn and Zaitsev (2000) suggested distinguishing two separate mineral species with the idealised formulae CaMn 4 [Si 5 O 15 ] and MnMn 4 [Si 5 O 15 ] under the conventional names ‘rhodonite-I’ and ‘rhodonite-II’, respectively.…”
“…A compilation of lattice constants for rhodonites, natural or synthetic, from the literature is given in Table 1. With one exception (rhodonite from Xanthi, Northern Greece [11]), a structure determination exists in all cases.…”
Section: Introductionmentioning
confidence: 99%
“…The description of a calcium-poor rhodonite from Xanthi (Greece) with the formula (Mn 4.56 Mg 0.22 Ca 0.15 Fe 0.03 )Si 5.02 O 15 [11] draws attention to a semiquantitative rhodonite analysis [13]. Chemical analyses of this special rhodonite from St. Salvator (Carinthia) were recalculated to the formula (Mn 4.60 Ca 0.18 Fe 0.12 Mg 0.11 ) (Si 4.93 Al 0.07 )O 15 [4].…”
Rhodonite from St. Salvator, Carinthia, Austria, with low calcium content and the formula (Mn 4.60 Ca 0.18 Fe 0.12 Mg 0.11 ) (Si 4.93 Al 0.07 )O 15 is characterized by the cell constants a 7.638(2), b 11.862(4), c 6.701(2) A Ê , 92.40(3), 94.23(3), 105.65(3) ; space group C 1 i À P " 1, Z 2. A re®nement of the structure afforded an R value of 0.033 for 3651 observed X-ray data (F o > 4'(F o )) and 237 variable parameters. The atomic arrangement exhibits a typical inosilicate structure in which (SiO 3 ) 5 chains are combined via MeO x polyhedra with x 6 or 7 to a framework. The mean hMe-Oi distances, the sum of bond valences for the Me positions, and the volumina for the MeO x Voronoi polyhedra are in accordance with the occupation of the individual atom positions determined by calculations from X-ray intensities. The coordination and deformation of the single MeO x polyhedra are characteristic for the structure type and not the result of substitutions of these Me positions by atoms with different ionic radii.
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