A blue sodic beryl from southeast Ireland

Abstract

Deep azure-blue beryl is reported from veins in Upper Devonian conglomerate from southeast Ireland. Microprobe analysis, MOssbauer spectroscopy and loss on ignition suggest an unusual chemistry with an exceptionally high degree of substitution of Fe and Mg for A1, and extreme amounts of Na and water held within channel sites in the structure. The calculated structural formula is:Be~.94(All.26Fe0. j sFe0 16Mg0.i2)S16.07Ois[Na0.45(H20)0.95]. Refractive indices (1.603 and 1.595) and the cell edge, a, (9.292 A) are also unusually high. Colourless beryl from the same locality, some of which forms cores to blue beryl prisms, has less octahedral substitution and a lower Fe/Mg ratio. The origin of the beryl is tentatively linked to contemporaneous volcanic activity.

Gemmological investigation of a synthetic blue beryl: a multi-methodological study

“…The channel content distributes over two extraframework sites: the first is occupied by water molecules (2a) and the second (2b) mainly by alkali cations (M site). Such partitioning agrees with those found in previous studies (Gibbs et al, 1968;Morosin, 1972;Hawthorne and Č erný, 1977;Brown and Mills, 1986;Evdokimova et al, 1989;Sanders and Doff, 1991;Artioli et al, 1993Artioli et al, , 1995Andersson, 2006;Gatta et al, 2006). The amount of water calculated by our structural refinements is comparable with that obtained by the weight-loss measurements and ranges from 0.40 to 0.49 molecules per formula unit (p.f.u.).…”

“…Alkali cations, water and carbon dioxide molecules often occupy 'extra-framework' sites, placed within the 6-membered ring channel parallel to [0001]. Several studies have been carried out on the crystal-chemistry and thermo-elastic behaviour of natural and synthetic beryls with a wide variety of extra-framework populations (Bragg and West, 1926;Nassau, 1967, 1968;Gibbs et al, 1968;Goldmann et al, 1968;Morosin, 1972;De Almeida et al, 1973;Hawthorne and Č erný, 1977;Aines and Rossman, 1984;Brown and Mills, 1986;Hazen et al, 1986;Aurisicchio et al, 1988;Evdokimova et al, 1989;Schmetzer, 1989;Sanders and Doff, 1991;Sheriff et al, 1991;Artioli et al, 1993Artioli et al, , 1995Charoy et al, 1996;Ferraris et al, 1999;Kolesov and Geiger, 2000;Prencipe, 2002;Č erný et al, 2003;Andersson, 2006;Gatta et al, 2006).…”

Crystal Chemistry of Dark Blue Aquamarine From the True Blue Showing, Yukon Territory, Canada

“…Values of c/a versus c from the powder diffraction data for sample GS2, compared with powder and single-crystal X-ray and neutron data from the recent literature. Symbols:  GS2, this study,  Pankrath & Langer (2002),  Viana et al (2002b),  Charoy et al (1996),  Artioli et al (1995), , Schmetzer & Bernhardt (1994),  Artioli et al (1993),  Duchi et al (1993),  Sanders & Doff (1991),  Sherriff et al (1991), a Aurisicchio et al (1988).…”

“…In particular, the c/a ratio is lower than the stated range of 0.991-0.996 for "octahedral" beryl where Al $ Me represents the main scheme of substitution (Aurisicchio et al 1988). The only samples with lower c/a values are the hydrous and sodic blue beryl from Ireland described by Sanders & Doff (1991) and the blue beryl from the Calcaferro mine described by Duchi et al (1993).…”

Aquamarine beryl from Zealand Station, Canada: a mineralogical and stable isotope study

“…The presence of excess silica is common when the Be-site (3 atoms) or Al-site (2 atoms) is assumed full to calculate the beryl formula (Sanders and Doff 1991;Abdalla and Mohamed 1999;Groat et al 2002;Černý et al 2003;. Excess silica can be assigned to the Be tetrahedron (Aurisicchio et al 1988) permitting the coupled substitution Be + 2Al = Si + 2(Fe, Mg) (Sanders and Doff 1991).…”