Miyawakiite-(Y), Mineral of the Year 2024

For 2024 the “Mineral of the Year” award has been assigned to miyawakiite-(Y). The mineral was discovered in an abandoned pegmatite mine located at Suishoyama, Iizaka village, Kawamata, Date District, Fukushima Prefecture, Japan, and was fully characterized by a Japanese research team lead by Daisuke Nishio-Hamane (Institute for Solid State Physics, University of Tokyo, Japan).
The pegmatite at the Suishoyama mine is rich in REE-bearing minerals, such as allanite-(Y) and britholite-(Y), plus carbonates such as caysichite-(Y) and tengerite-(Y). Miyawakiite-(Y) and the other carbonates occur as the secondary minerals formed by supergene alteration of allanite-(Y) and britholite-(Y). Miyawakiite-(Y) is the third mineral having the Suishoyama pegmatite as the type locality, besides britholite-(Y) (1938) and iwashiroite-(Y) (2003). The approximate GPS coordinates are 37°40’ N, 140°37′ E.
At the type locality miyawakiite-(Y) occurs as thin plates or columnar crystal with a pale yellow colour, transparent with a vitreous lustre, with dimensions typically ranging from 0.2 to 0.5 mm. The.
The ideal chemical formula of miyawakiite-(Y) is □Y₄Fe²⁺₂(Si₈O₂₀)(CO₃)₄(H₂O)₃. In the empirical formula K partially substitutes for vacancy, other REEs and Ca partially substitute for Y, Mg and Mn²⁺ partially substitute for Fe²⁺. Miyawakiite-(Y) is chemically related to caysichite-(Y), both being silicate minerals including REEs and carbonate groups. However the two minerals have different crystal structures.

The unprecedented crystal structure of miyawakiite-(Y) has been solved and refined up to R = 3.86% in the tetragonal space group I4/mcm. Its unit-cell parameters are a = 17.53637(9) Å, c = 9.55702(8) Å, V = 2939.02(4) Å3, Z = 4. The structure is quite unique: a Y- and Fe-centered polyhedral arrangement with CO₃ triangles forms a prismatic framework, with channels developing along the c axis. A SiO₄ tetrahedral network occurs in this channel, forming a zeolite-like framework with larger sites inside, mostly vacant and only partially occupied by K.
The mineral took its name after Ritsuro Miyawaki (b. 1959), mineralogist at the National Museum of Nature and Science, Tsukuba, Ibaraki, Japan, for his lifetime contribution to the systematic mineralogy, with a special attention to REE-bearing minerals. Ritsuro Miyawaki described some 30 new mineral species. Besides, Ritsuro Miyawaki provided a tremendous service to Mineral Sciences serving (-2018) as the national representative for Japan within the IMA Commission on New Minerals, Nomenclature and Classification. In 2018 Ritsuro Miyawaki was appointed as chair of the CNMNC for the 2018-2022 period. During his four-year tenure he evaluated more than 500 proposed new minerals.
The full description of the new mineral has been published in the Journal of Mineralogical and Petrological Sciences [Nishio-Hamane, D., Momma, K., Shimobayashi, N., Ohnishi, M., Kobayashi, T. (2024): Miyawakiite–(Y), □Y₄Fe₂(Si₈O₂₀)(CO₃)₄(H₂O)₃, a new mineral from Suishoyama, Kawamata Town, Fukushima Prefecture, Japan].

Link to the original article:
Journal of Mineralogical and Petrological Sciences (2024) 119: 023