Niobokupletskite, a New Astrophyllite-Group Mineral From Mont Saint-Hilaire, Quebec, Canada: Description and Crystal Structure

Abstract

Niobokupletskite is a new member of the astrophyllite group found in nepheline syenite pegmatites at Mont Saint-Hilaire, Quebec, in association with aegirine, albite, analcime, calcio-ancylite-(Ce), calcite, catapleiite, epididymite, fluorite, genthelvite, microcline, natrolite, pyrochlore, rhodochrosite and wurtzite. It is transparent, with a vitreous luster, brittle with a perfect {001} cleavage, and has an uneven to splintery fracture. Niobokupletskite is biaxial positive, ␣ 1.718 (1) SOMMAIRELa niobokupletskite est une nouvelle espèce minérale, membre du groupe de l'astrophyllite, que l'on retrouve dans les pegmatites syénitiques à néphéline du Mont Saint-Hilaire, Québec, en association avec aegyrine, analcime, calcite, catapléite, épididymite, fluorite, genthelvite, microcline, natrolite, pyrochlore, rhodochrosite et wurtzite. C'est un minéral transparent, avec éclat vitreux, cassant, avec un clivage {001} parfait et une fracture irrégulière à fibreuse. La niobokupletskite est biaxe positive, avec ␣ 1.718(1), ␤ 1.733(1), ␥ calc 1.750(1), 2V observé = 87(2)°. Le minéral est triclinique, groupe spatial P1, avec paramètres réticulaires a 5.4303(9), b 11.924(2), c 11.747 (2)

Astrophyllite-group minerals from the Ilímaussaq complex, South Greenland (contribution to the mineralogy of Ilímaussaq no. 123)

“…(6) Some analyses plot very close to the field of niobokupletskite (Fig. 3a), a phase so far recorded only from Mont St Hilaire, Québec (Piilonen et al, 2000). Given the agpaitic nature of both complexes, niobokupletskite may also be present at Ilímaussaq.…”

“…As Piilonen et al (2003) have pointed out, problems associated with these schemes include the absence of charge balance, the creation of vacancies and the incorporation of Fe 2+ and Fe 3+ into the D site, for which there is no structural or compositional support. Piilonen et al (2000) proposed that the incorporation of Nb into the structure of niobophyllite (and niobokupletskite) was best modelled by the coupled substitution Ti + F (or OH) > Nb + O.…”

“…Compositional variation in Nb-rich members of the astrophyllite group. Data used are the new average Ilímaussaq analyses (this paper, Table 2, only analyses with F), the type niobophyllite (Nickel et al, 1964;Piilonen et al, 2003), and the type niobokupletskite (Piilonen et al, 2000(Piilonen et al, , 2003 (Table 3), although the SiO 2 content, at 33.43 wt.%, is not as low as in the type material. Ryka (1994) mentioned the presence of 'hydroastrophyllite' in the Ełk syenite massif, Poland, but presented no analyses.…”

Crystal-structure refinement of a Zn-rich kupletskite from Mont Saint-Hilaire, Quebec, with contributions to the geochemistry of zinc in peralkaline environments

“…A similar situation exists in Zn-rich kupletskite, where sheets of (Mn,Zn)(O,OH) 6 octahedra which display extensive Zn > Mn isomorphism, are sandwiched between heterogeneous sheets consisting of [Si 4 O 12 ] 8 À cross-linked by (Ti,Nb)f 6 octahedra. At Mont Saint-Hilaire, Znrich kupletskite and Zn-rich niobokupletskite are often associated with wurtzite, the low-f S 2 ZnS polymorph, whereas Zn-free species are associated with sphalerite, the high-f S 2 ZnS polymorph (Scott and Barnes, 1972;Piilonen et al, 2000), suggesting that incorporation of Zn into the AGM structure is a function of f S 2 and not a function of temperature as both polymorphs are stable over a wide range of temperatures (Scott and Barnes, 1972). The presence or absence of Zn silicate in an alkaline environment is a complex indicator of f S 2 , f O 2 and alkalinity.…”

“…Introduction KUPLETSKITE, ideally K 2 NaMn 7 Ti 2 Si 8 O 26 (OH) 4 F, a member of the heterophyllosilicate astrophyllite-group, was first described by Semenov (1956) from nepheline syenite pegmatites in the Lepkhe-Nelm and Kuivchorr mountains of the Lovozero massif, Kola Peninsula, Russia. Since then, it has been found in a variety of SiO 2 -oversaturated and SiO 2 -undersaturated alkaline intrusions including the Burpala massif, Siberia, Russia (Chukrov, 1972), Point of Rocks, New Mexico, USA (DeMark, 1984), Gjerdingen, Norway (Raade and Haug, 1982), the Junguni intrusion, Chilwa, Malawi (Woolley and Platt, 1988), Khibiny massif, Kola Peninsula, Russia (Kostyleva-Labuntsova et al, 1978), the Mariupol complex, Azov sea region, Ukraine (Valter et al, 1965), the Larvik complex, Langesundsfjord area, Norway (Piilonen et al, 2003a), the Werner Bjerge complex and Kangerdlugssuaq, East Greenland (Brooks et al, 1982;Christiansen et al, 1998), Mont Saint-Hilaire, Québec, Canada (Horváth and Gault, 1990;Piilonen et al, 2000Piilonen et al, , 2003a, Zaangarskii massif, Siberia, Russia (Sveshnikova et al, 1976), and the Tamazeght complex, High Atlas mountains, Morocco (Kadar, 1984). Kupletskite generally occurs as a rare primary to post-magmatic mineral in alkaline pegmatites and late-stage vugs.…”