Tetsuo Minakawa

Imayoshiite, Ca3Al(CO3)[B(OH)4](OH)6·12H2O, a new mineral of the ettringite group from Ise City, Mie Prefecture, Japan

Abstract Imayoshiite, Ca3Al(CO3)[B(OH)4](OH)6 ·12H2O, occurs in cavities in the altered gabbro xenolith in the sepentinized dunite exposed at Suisho-dani, Ise City, Mie Prefecture, Japan. Imayoshiite is colourless and transparent with a vitreous lustre and its aggregates are white with a silky lustre. Imayoshiite has a white streak. Its Mohs hardness is 2-3. It is brittle, the cleavage is distinct on {100} and the fracture is uneven. The mineral is uniaxial (-) with the indices of refraction ω = 1.497(2) and ε = 1.470(2) in white light. Imayoshiite is hexagonal, P63, a = 11.0264(11), c = 10.6052(16) Å by powder diffraction and a = 11.04592(2), c = 10.61502(19) Å by single-crystal diffraction. The structural refinement converged to R1 = 2.35%. Imayoshiite is the first member of the ettringite group with both CO3 and B(OH)4 anions.

Vanadoallanite-(La): a new epidote-supergroup mineral from Ise, Mie Prefecture, Japan

Abstract The new mineral, vanadoallanite-(La), found in the stratiform ferromanganese deposit from the Shobu area, Ise City, Mie Prefecture, Japan, was studied using electron microprobe analysis and single-crystal X-ray diffraction methods. Vanadoallanite-(La) is a rare-earth element-rich monoclinic epidote-supergroup mineral with simplified formula CaLaV3+AlFe2+(SiO4)(Si2O7)O(OH) (Z = 2, space group P21/m) characterized by predominantly V3+ at one of three octahedral sites, M1. The crystal studied shows large V (~8.4 V2O3 wt.%), Fe (~13.8 Fe2O3 wt.%; Fe2+/total Fe = 0.58) and Mn (~8.8 MnO wt.%) contents. A small amount of Ti is also present (~1.3 TiO2 wt.%). Structural refinement converged to R1 = 2.96%. The unit-cell parameters are a = 8.8985(2), b = 5.7650(1), c = 10.1185(2) Å, β = 114.120(1)° and V = 473.76(2) Å3. The cation distributions determined at A1, A2 and M3 are Ca0.61Mn0.39, (La0.46Ce0.14Pr0.07Nd0.18)∑0.85Ca0.15 and Fe0.562+Mn0.302+Mg0.06V0.053+Fe0.033+, respectively. On the other hand, depending on Ti assignment, two different schemes of the cation distribution at M1 and M2 can be considered: (1) M1(V0.583+Fe0.343+Ti0.084+)M2(Al0.92Fe0.083+), and (2) M1(V0.583+Fe0.423+)M2(Al0.92Ti0.084+). In both cases, the dominant cations at A1, A2, M1, M2 and M3 are Ca, La, V3+, Al and Fe2+, respectively. According to ionic radius, Ti4+ possibly prefers M2 rather than Fe3+. A large Mn2+ content at A1 also characterizes our vanadoallanite-(La). The structural change of Mn2+-rich allanite-group minerals is considered to be controlled by two main factors. One is the large Mn2+ content at A1 in vanadoallanite-(La), which modifies the topology of the AlO9 polyhedron. The other is the expansion of M3O6 and M1O6 octahedra caused by large octahedral cations, such as Fe2+ and Mn2+, at M3 and the trivalent transition elements, V3+ and Fe3+, at M1.

Sursassite: Hydrogen bonding, cation order, and pumpellyite intergrowth

Abstract The crystal chemistry of sursassite, simplified formula Mn2+2 Al3Si3O11(OH)3, from six different localities [(1) Falotta, Switzerland, (2) Woodstock, New Brunswick, Canada, (3) Kamisugai, Japan, (4) Kamogawa, Japan, (5) Molinello, Italy, and (6) Gambatesa, Italy] was studied using electron microprobe analysis (EMPA), Fourier transform infrared spectroscopy (FTIR), and single-crystal X-ray diffraction methods. The structure has two symmetry independent Mn sites. The Mn1 site is seven coordinated by O and hosts, in addition to Mn2+, up to 20% Ca, whereas Mn2 has octahedral coordination and is strongly selective for Mn2+. In the simplified formula, three smaller octahedral M sites are occupied by Al. However, M1 also accepts significant amounts of divalent cations, such as Cu, Mg, Fe, and Mn, whereas M2 is occupied exclusively by Al. The unit-cell parameters of sursassite are a = 8.698-8.728, b = 5.789-5.807, c = 9.778-9.812 Å, β = 108.879-109.060°, V = 465.7-470.0 Å3, the space group is P21/m. Structure refinements converged to R1 values of 2.15-6.62%. In agreement with bond-valence analyses, at least three OH groups, depending on the concentration of divalent cations at M1, are found at the O6, O7, and O11 positions. However, the bond-valence sum at O10 is always low, thus partial hydroxylation is assumed at O10 to maintain charge balance. Owing to the influence of divalent cations at M1 in sursassite the hydrogen-bond systems in sursassite and isostructural macfallite are different. The FTIR spectrum in the region of OH-stretching vibrations is characterized by three strong bands at 3511, 3262, and around 2950 cm-1, the latter being broad. The band at 2950 cm-1 is assigned to strong hydrogen bonds between O6 and O10 (O6···O10 = 2.66 Å). Residual difference-Fourier peaks in the refinement of the Kamogawa and Molinello (specimen 1) crystals indicated less than 5% pumpellyite intergrowth.

Ferriakasakaite-(La) and ferriandrosite-(La): new epidote-supergroup minerals from Ise, Mie Prefecture, Japan

Abstract The new REE-rich, monoclinic, epidote-supergroup minerals ferriakasakaite-(La) and ferriandrosite-(La), found in tephroite ± calcite veinlets cutting the stratiform ferromanganese deposit from the Shobu area, Ise City, Mie Prefecture, Japan, were studied using electron microprobe analysis and single-crystal X-ray diffraction methods. Ferriakasakaite-(La), ideally A1CaA2LaM1Fe3+M2AlM3Mn2+ (SiO4)(Si2O7)O(OH) (Z = 2, space group P21/m), has a new combination of dominant cations at A1(Ca) and M3(Mn2+), which are the key sites to determine a root name for epidote-supergroup minerals. The unit-cell parameters are a = 8.8733(2), b = 5.7415(1), c = 10.0805(3) Å, β = 113.845(2)º and V = 469.73(2) Å3. According to the structural refinement (R1 = 3.13%), the determined structural formula is A1(Ca0.54Mn2+ 0.46) A2[(La0.48Ce0.20Pr0.07Nd0.18Gd0.02)∑0.95Ca0.05]M1(Fe3+0.42V3+0.34Al0.18Ti4+0.06)M2(Al0.96Fe3+0.04) M3(Mn2+0.50Fe2+0.43Mg0.07)(SiO4)(Si2O7)O(OH).Ferriandrosite-(La), ideally A1Mn2+A2LaM1Fe3+M2AlM3Mn2+(SiO4)(Si2O7)O(OH) (Z = 2, space group P21/m), is the M1Fe3+ analogue of androsite. The unit-cell parameters are a = 8.8779(1), b = 5.73995(1), c = 10.0875(2) Å, β = 113.899(1)° and V = 469.97(2) Å3, and the structural formula is A1(Mn2+0.56Ca0.44) A2[(La0.49Ce0.20Pr0.08Nd0.19Gd0.02)∑0.97Ca0.03]M1(Fe3+0.40V3+0.28Al0.20Fe2+0.05Ti4+0.07)M2(Al0.97Fe3+0.03) M3(Mn2+0.50Fe2+0.40Mg0.10)(SiO4)(Si2O7)O(OH) (R1 = 2.93%). The two new minerals, which are compositionally very similar overall, are distinguished by occupancy of A1, Ca vs. Mn2+. The structural properties of these minerals depend not only on the REE content at A2, but also on the Mn content at A1.

Iyoite, MnCuCl(OH)3 and misakiite, Cu3Mn(OH)6Cl2: new members of the atacamite family from Sadamisaki Peninsula, Ehime Prefecture, Japan

Abstract Two new members of the atacamite family were discovered recently in the Sadamisaki Peninsula, Ehime Prefecture, Japan. Iyoite, MnCuCl(OH)3, is an Mn-Cu ordered analogue of botallackite, while misakiite, Cu3Mn(OH)6Cl2, is an Mn-rich analogue of kapellasite. Both minerals occur in manganese ore crevices in close association with one another. Iyoite forms radial and dendritic aggregates consisting of pale green, bladed crystals. Misakiite commonly exists in emerald green, tabular, hexagonal crystals. The densities of iyoite and misakiite were calculated to be 3.22 and 3.42 g cm−3 based on their empirical formulae and powder X-ray diffraction data. Under the same axial setting of botallackite, iyoite is monoclinic, space group P21/m, a = 5.717(2), b = 6.586(2), c = 5.623(3) Å, β = 88.45(3)° and V = 211.63(15) Å3. Misakiite is trigonal, space group P3̅m1, with a = 6.4156(4), c = 5.7026(5) Å and V = 203.27(3) Å3. The structures of both minerals are classified as layer type and the two are closely related. These new minerals were formed by the reaction between seawater and naturally-occurring manganese ores including native copper. These minerals are challenging to produce synthetically. Misakiite was synthesized successfully using a hydrothermal method, while iyoite could not be made.