Anomalous optical variations in the grossular garnet from the Eden Mills, Belvidere Mountain (Vermont, USA)

Rietveld crystal structure refinement of a natural rhombohedral grossular-andradite garnet from Serbia

“…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).…”

Structural dissymmetrization of optically anisotropic Grs64±1Adr36±1Sps2grandite from Meka Presedla (Kopaonik Mt., Serbia)

“…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).…”

Orthorhombic Crystal Structure of Grossular Garnet (Suva Česma, Western Serbia): Evidence from the Rietveld Refinement

“…We believe that the weak garnet anisotropy could indicate the presence of disymmetrization; there are five possible causes of this, discussed in [4][5][6]. In summary, it is agreed that the that grossular-andradite garnet group could exhibit non-cubic symmetry in various space groups (hereinafter, s.g.'s), such as: I‾1 [9][10][11][12][13][14]; Fddd [9,12,15,16]; Fddd or C2/c [17]; R‾3c or Fddd [5]; and R‾3c [6]. More recently, it was shown that these minerals could have a tetragonal symmetry (most likely I41/a s.g.), as well [18].…”

“…characteristics align this sample further into a group that includes only a few orthorhombic garnets within the grossular-andradite solid-solution series, and the first occurrence of such a garnet in Serbia. The five previously studied orthorhombic specimens were extracted from Moravia (Czechoslovakia) and Kamaishi (Japan) [9], Hortsavinya (Spain) [15], Bazhenovskoe (Russia) [12], and Eden Mills (USA) [16]. There is also one birefringent uvarovite from Saranov (Russia) that belongs to the same orthorhombic Fddd space group [30].…”