Nomenclature of the gadolinite supergroup

Abstract

The newly defined gadolinite supergroup approved by the IMA CNMNC (vote 16-A) includes mineral species that have the general chemical formula A 2 MQ 2 T 2 O 8 ' 2 and belong to silicates, phosphates and arsenates. Each site is occupied by: A À Ca, REE (Y and lanthanoids), actinoids, Pb, Mn 2þ , Bi; M À Fe, □ (vacancy), Mg, Mn, Zn, Cu, Al; Q À B, Be, Li; T À Si, P, As, B, Be, S; and ' À O, OH, F. The classification of the gadolinite supergroup is based on the occupancy of A, M, Q, T and ' sites and application of the dominant-valency and dominant-constituent rules. The gadolinite supergroup is divided into two groups defined by prevailing charge occupancy at the T site À Si 4þ in gadolinite group and P 5þ or As 5þ in herderite group. The gadolinite group is divided into the gadolinite and datolite subgroups. The A site is dominantly occupied by divalent cations in the datolite subgroup and by trivalent cations in the gadolinite subgroup. Accordingly, the Q site is dominantly occupied by B 3þ in the datolite subgroup and by Be 2þ in the gadolinite subgroup. The herderite group is divided into two subgroups. The herderite subgroup is defined by the dominant divalent cation (usually Ca 2þ ) in the A site and Be 2þ in the Q site, while the M site is vacant. The drugmanite subgroup is defined by the dominance of divalent cations (usually Pb 2þ ) in the A site, vacancy in the Q site and the occupation of the M site. Moreover, "bakerite" is discredited as mineral species because it does not meet the conditions of the dominant-constituent rule.

Low-Temperature Crystal Chemistry of Hingganite-(Y), from the Wanni Glacier, Switzerland

“…EDX spectra were obtained under the following conditions: 20 kV accelerating voltage, 1 nA beam current, and matrix correction by the extended Pouchou and Pichoir (XPP) method [54]. The empirical formula was calculated by two methods suggested for the gadolinite supergroup by Bačík et al [4]: (1) sum of cations at the A site equals 2 or (2) sum of cations at the T site equals 2 ( Table 1). Content of BeO and B 2 O 3 was calculated according to recommendations [4].…”

“…The empirical formula was calculated by two methods suggested for the gadolinite supergroup by Bačík et al [4]: (1) sum of cations at the A site equals 2 or (2) sum of cations at the T site equals 2 ( Table 1). Content of BeO and B 2 O 3 was calculated according to recommendations [4]. The B:Be ratio was calculated based on Demartin et al [33] using bond lengths data of the QO 4 (Q = B, Be) tetrahedra obtained from SCRXD analysis.…”

“…According to the modern nomenclature [4], the general formula of the gadolinite supergroup is A 2 MQ 2 T 2 O 8 φ 2 , where A = Ca, rare-earth element (REE) (Y and lanthanoides), Bi; M = Fe 2+ , (vacancy), Mg, Mn, Zn, Cu, Al, Fe 3+ ; Q = B, Be, Li; T = Si, B, Be, S, P, and φ = O, OH, F. The monoclinic (P2 1 /c) structure of the gadolinite-supergroup minerals can be described as layered, consisting of two different layers parallel to (100) and alternating along the (100) direction. Anion layers of [QTO 4 (φ)] 3-are formed by four-and eight-membered rings of corner sharing QO 4 and TO 4 tetrahedra and cation layers formed by AO 8 polyhedra with square antiprism geometry and MO 6 octahedra.…”

“…Based on the B:Be:Li ratio, the gadolinite group is further divided into three subgroups: The gadolinite (Q 2 = Be 2 ), the datolite (Q 2 = B 2 ), and one hypothetical subgroups (Q 2 = BeLi). There are 8 minerals in the gadolinite subgroup: gadolinite-(Y), gadolinite-(Ce), gadolinite-(Nd), minasgeraisite-(Y), hingganite-(Y), hingganite-(Yb), hingganite-(Ce), and the recently discovered hingganite-(Nd) [4][5][6][7][8][9][10][11][12]. Mineral species can be identified based on the A Ca/sum of the A-site cations ratio [4] and the prevailed REE.…”

Gadolinite-(Nd), a new member of the gadolinite supergroup from Fe-REEdeposits of Bastnäs-type, Sweden

“…The newly-defined gadolinite supergroup (Bačík et al, 2017) , Zn, Cu, Al; Q: Be, B > Li; T: Si > P, As, B, Be, S; j: O, OH > F (Bačík et al, 2017). Based on the T-site occupancy, the gadolinite supergroup is divided into the gadolinite [Si 4+ > (P 5+ + As 5+ )] and herderite [(P 5+ + As 5+ ) > Si 4+ ] groups.…”