Chlorine-rich potassium hastingsite from West Ongul Island, Lützow–Holm Bay, East Antarctica

Abstract

Chlorine-rich potassium hastingsite occurs in a calcareous pegmatite, a replacement zone and an amphibolite lens within hornblende gneiss on West Ongul Island, Lützow-Holm Bay, East Antarctica. The amphibolite lens and hornblende gneiss were metamorphosed to the kyanite-sillimanite grade of the granulite facies during Proterozoic metamorphism. Chemical analysis (3.27 wt.% Cl), unit cell parameters and optical properties of the Cl-rich potassium hastingsite are given. Cl-rich (> 3 wt.%) calcic amphiboles reported from various rock types are mostly more than 0.9 in (Na+ K) content, more than 0.4 in K/(Na + K) ratio, more than 0.75 in Fe2+/(Fe2++ Mg + Mn) ratio and more than 1.9 in AlIVcontent (total iron as FeO and O = 23). The unit cell volume of Cl-rich hastingsite is distinctly larger than that of Cl-poor hastingsite.

Effect of chlorine on the crystal structure of a chlorine-rich hastingsite

“…The calcareous pegmatite was formed during Proterozoic metamorphism, and is composed of Cl-rich hastingsite, scapolite, calcite and actinolite, with accessory analcite, titanite, apatite, quartz and pyrite (Suwa et al, 1987).…”

“…CALClC amphibole with CI replacing OH occurs in metamorphic, plutonic and volcanic rocks (Suwa et al, 1987). The highest content of CI recorded so far is 7.24 wt.% in a calcic amphibole from a skarn in Dashkesan (Krutov, 1936).…”

“…Suwa et al (1987) pointed out that the Cl-rich hastingsites are high in A1 iv and (Na + K) contents and K/(Na + K) value. The chemical behaviour of Cl-rich amphiboles has been interpreted from a structural point of view by Ito and Anderson (1983), Volfinger et al (1985), Suwa et aL (1987), and Yamaguchi (1989).…”

Potassic-ferropargasite, a new member of the amphibole group, from Kabutoichiba, Mie Prefecture, central Japan

“…Table 6. Bond -valence sums weighted on the occupancies for potassic -ferropargasite control on Cl content in calcic amphibole has been discussed by many authors (e.g., Suwa et al, 1987;Morrison 1991;Enami et al, 1992;Sato et al, 1997). Makino et al (1993) and Oberti et al (1993) revealed the crystal structures of Cl -and K -rich hastingsite and ferropargasite.…”

“…Constructive reviews by Prof. S. Kobayashi and Dr. [4] Al and Cl of K -rich calcic amphiboles with [4] Al ≥ 1.5 apfu and [A] (Na + K) ≥ 0.5 apfu. The chemical data are from Borley (1963), Krutov and Vinogradova (1966), Leelanandam (1970), Czamanske et al (1977), Hawthorne and Grundy (1977), Dick and Robinson (1979), Sharma (1981), Shimazaki et al (1984), Matsubara and Motoyoshi (1985), van Marcke de Lummen and Verkaeren (1985), Gulyaeva et al (1986), Suwa et al (1987), Sawaki (1989), Morrison (1991), Enami et al (1992), Oberti et al (1993), Shira ishi et al (1994, Deer et al (1997), Robinson et al (1997), Sato et al (1997), Sokolova et al (2000), Chukanov et al (2002), Mazdab (2003), Banno et al (2004), Pekov et al (2005), Korinevskiy and Korinevskiy (2006), Sautter et al (2006) and Banno et al (this study). The Cl contents of K -rich amphiboles described by Shimazaki et al (1984) and Sawaki (1989) were not given, but they pointed out that qualitative analyses of these amphiboles show no appreciable amount of chlorine.…”