THE CRYSTAL CHEMISTRY OF Al-RICH AMPHIBOLES: SADANAGAITE AND POTASSIC-FERRISADANAGAITE

Abstract

The crystal structures of magnesiosadanagaite (MS) from Mogok, Myanmar, monoclinic, a 9.857(2), b 17.899(4), c 5.318(1) Å, b 105.36(1)°, V 904.74(8) Å 3 , C2/m, Z = 2, and potassic-ferrisadanagaite (FS) from the Ilmen alkaline massif, South Urals, Russia, a 9.9257(4), b 18.0917(7), c 5.3709(2) Å, b 105.19(1)°, V 930.75(2) Å 3 , C2/m, Z = 2, have been refined to R values of ~3% using single-crystal MoKa X-ray data. The crystals used in the collection of the intensity data were subsequently analyzed by electron-microprobe techniques, leading to the following compositions: MS: (Na 0.82 K 0.17) (Ca 1.95 Na 0.05) (Mg 3.36 Fe 2+ 0.23 Al 1.20 Cr 3+ 0.07 Ti 4+ 0.16) (Si 5.47 Al 2.53) O 22 [(OH) 1.58 F 0.42 ]; FS: (Na 0.31 K 0.62) (Ca 1.72 Na 0.28) (Mg 0.56 Fe 2+ 2.12 Mn 2+ 0.26 Zn 0.02 Al 0.72 Fe 3+ 1.07 Ti 4+ 0.21) (Si 5.24 Al 2.76) O 22 [(OH) 1.70 F 0.30 ]. Site populations were assigned from the results of site-scattering refinement and stereochemical analysis, taking into account the unit formula determined for each crystal. The <T-O> distances, 1.678 and 1.684 Å, indicate that [4] Al is strongly ordered at the T(1) site in each crystal, but the <T(2)-O> distances, 1.648 and 1.655 Å, indicate significant Al at the T(2) site. The Fe 2+ and Fe 3+ contents in each crystal were assigned from the <M-O> distances. The A(2) and A(m) sites are occupied by Na and (Na,K), respectively, in crystal MS, and by Na and K, respectively, in crystal FS. Both amphiboles show SRO (short-range order) of species at the M(4), O(3), A(m) and A(2) sites, and the relative abundances of these arrangements were assigned.

Formation process of Al-rich calcium amphibole in quartz-bearing eclogites from The Sulu Belt, China

“…SiO 2 -undesaturated lithologies as summarized inMogessie et al (1986),Hawthorne and Harlow (2008), and the current study. These limited modes of occurrences might indicate This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change.…”

Kôzulite, an Mn-rich alkali amphibole

“…Our results on kôzulite are very similar to those observed by Hawthorne et al (1995) uncertainties. The presence of two distinct A sites on the mirror plane, A(m) and A(m)′ has also been observed in many other alkali amphiboles (e.g., Hawthorne et al 1996;Hawthorne and Harlow 2008).…”

“…For the initial structural refinement of kô zulite, see: Fleischer & Nickel (1970); Kitamura & Morimoto (1972). For general background to the amphibole group, see: Hawthorne (1983); Hawthorne et al (1995Hawthorne et al ( , 1996; Hawthorne & Harlow (2008). For background information on the amphibole group and nomenclature, see: Leake (1978); Leake et al (1997Leake et al ( , 2003; Mogessie et al (2004).…”

“…The total Mn and Mg in the M1 + M2 + M3 sites were fixed to those from the chemical analysis. To dampen the extreme correlations that would otherwise occur among the refined A-site variables, the isotropic displacement factors of these A sites were constrained to be equal (Hawthorne & Harlow 2008). Refinement.…”

Age, petrogenesis, and metamorphic modelling of high‐pressure garnet‐amphibolite from the Tethyan Himalayan Sequence of Bhagirathi Valley, Western Garhwal Himalaya

“…Amphibole are calcic in nature. Classification diagram of amphibole on the basis of calculated ions from EPMA analysis of major oxides in the garnet‐amphibolite (M1) (after Hawthorne, 1981) suggests that they can be classified as tschermakite (Figure 4a). Amphibole (tschermakite) shows moderate variation of Mg and Ca ( X Mg = 0.53–0.58 and X Ca = 0.77–0.80).…”