2026 Volume 121 Issue 1 Article ID: 260301
Horiite is a new member of the bafertisite group within the seidozerite supergroup, discovered at the Taguchi mine in Aichi Prefecture, Japan. The mineral was named in honor of Dr. Hidemichi Hori (1934-2019), a distinguished Japanese mineralogist and founder of Hori Mineralogy, Ltd. Horiite crystals are thin, elongated plates with long axes up to 300 µm in length and 20 µm in thickness. They are closely layered and tend to aggregate, sometimes forming aggregates with hejtmanite. The Mohs hardness of horiite is 4-5, its tenacity is brittle, and its calculated density is 4.08 g·cm−3. Under plane-polarized light, the mineral shows very weak pleochroism, changing from nearly colorless to pale brown. The empirical formula, calculated on the basis of 24 O and 2 (OH + F) atoms per formula unit, is (Ba1.98Sr0.01)Σ1.99(Mn1.97Ca0.04)Σ2.01(Mn3.34Fe0.36Mg0.31)Σ4.01(Ti1.98Sn0.03)Σ2.01Si4.00P1.99O24[(OH)1.92F0.08]Σ2, ideally Ba2Mn2Mn4Ti2(Si2O7)2(PO4)2O2(OH)2. The refined unit-cell parameters determined by single-crystal X-ray diffraction are a = 5.35090(10) Å, b = 13.89170(10) Å, c = 14.2777(2) Å, α = 98.7260(10)°, β = 93.8420(10)°, γ = 90.0570(10)°, and V = 1046.60(3) Å3, and Z = 2, in conjunction with space group P1 (#2), whereas the lattice parameters determined by synchrotron-radiation powder X-ray diffraction are a = 5.3349(9) Å, b = 13.884(2) Å, c = 14.270(3) Å, α = 98.785(15)°, β = 93.836(16)°, γ = 90.029(16)°, and V = 1043.7(3) Å3. Although the crystal structure of horiite is partially related to that of yoshimuraite, it represents a new structural type. Consequently, according to the nomenclature concept of the seidozerite supergroup, the crystal structure of horiite is identified as the fifth basic structure within the bafertisite group. Horiite is the only species among more than 50 in the seidozerite supergroup that contains species defining Mn-occupied sites in the I block.
The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists
The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists
