The ETn homologous row of the epidote–törnebohmite polysomatic series is considered, which includes minerals of the epidote (n = 0) and gatelite (n = 1) supergroups and radekškodaite group (n = 2). The crystal structures of members of the series are based upon the alternation of epidote (E) and törnebohmite (T) two-dimensional modules. The aristotype structure types of the members of the row crystallise in the P21/m space group with the unit-cell parameters a ≈ 8.90, b ≈ 5.65, c ≈ (10.10 + 7.50n) Å, β ≈ 116.5° and V ≈ (455 + 338n) Å3. The general formula for the members of the row can be expressed as A2(n+1)Mn+3[Si2O7][SiO4]2n+1Xn+2 (X = O, OH and F). The structure model for the hypothetical ET3 member of the series is constructed and the general formulae are derived for the calculation of the number of atoms per unit cell and the number and multiplicities of the atom sites for any value of n. The concept of K-sequence is introduced that is analogous to the concept of a Wyckoff sequence. The general formulae for the information-based complexity parameters are derived for the ETn homologous row of the epidote–törnebohmite polysomatic series with different parities of n. The present absence of the members of the series with n > 2 reflects the entropic restrictions on the polysomatic series that confirm the principle of maximal simplicity for modular inorganic structures.

Puttapaite, Pb2Mn2+2ZnCr3+4O2(AsO4)4(OH)6·12H2O, is a new mineral from the Beltana deposit, Puttapa, Flinders Ranges, South Australia, Australia. It forms rosette-like aggregates to 50 micrometers across composed of diamond-shaped tablets to 45 micrometers in length and 5 micrometers in thickness. Crystals are flattened on {001} and the observed forms are {001} and {110}. The calculated density is 3.562 g/cm–3. Optically, puttapaite is biaxial (−) with α = 1.700(5), β = 1.720(5), γ = 1.730(5) and 2V (meas.) = 67(1)°. Electron microprobe analyses gave the empirical formula (based on 36 oxygen atoms pfu) Pb1.96(Mn2+1.52Ca0.28Sr0.22)Σ2.02(Zn0.40Mg0.39Cu0.15)Σ0.94(Cr3+2.89Al0.45Fe3+0.40,Mn3+0.26)Σ4.00O2[(AsO4)3.71(Cr6+O4)0.29]Σ4.00(OH)6.13·11.87H2O. Puttapaite is monoclinic, C2/m, with a = 12.405(3), b = 10.565(2), c = 12.311(3) Å, β = 106.06(3)°, V = 1550.4(6) Å3 and Z = 2.

The structure was solved using synchrotron single-crystal X-ray diffraction data and refined to R1 = 0.1189 on the basis of 915 observed reflections with F0 > 4σ(F0). Puttapaite has a unique structure that consists of M4O16 clusters that share corners with TO4 tetrahedra, which in turn share corners with M1 octahedra in the [010] direction. Clusters link in the [001] direction via corner sharing M2 octahedra to form sheets parallel to {100}. Pb anions lie between the sheets.

Utilising Y2O3, Sm2O3, LuPO4, and EuPO4 and a 2N NaOH solution, Y, Sm, Lu, and Eu are metasomatically incorporated into a natural, inclusion-free, almandine–pyrope garnet (Gore Mountain) at 900°C and 1000 MPa (sealed Pt capsule, CaF2 setup with graphite oven, piston cylinder press) via a coupled dissolution–reprecipitation process. Incorporation of Y+REE takes place via a series of coupled substitutions involving the dodecahedral site in garnet, i.e. VIII(Y,REE)3+ + IVAl3+ = VIII(Fe,Mg,Mn,Ca)2+ + IVSi4+; 2VIII(Y+REE)3+ + VIII□ = 3 VIII(Fe,Mg,Mn,Ca)2+; VIII(Y,REE)3+ + VIIINa+ = 2 VIII(Fe+Mg+Mn+Ca)2+; and VIII(Y,REE)3+ + VI(Fe,Mg)2+ = VIII(Fe,Mg)2+ + VI(Al,Fe)3+. In comparison to the slower, solid-state diffusion of Y+REE in garnet under high-grade (700–900°C; 500–1000 MPa) conditions, the results from these experiments indicate that efficient, rapid incorporation (or depletion) of Y+REE in garnet could occur by fluid-aided coupled dissolution–reprecipitation during metamorphism. The results from these experiments have important implications with regard to the effect of metasomatic/metamorphic events on Lu-Hf and Sm-Nd age determination in garnet, the use of Y exchange between xenotime and garnet as a geothermometer in metamorphic rocks, and the effect of metamorphic fluids on the coupling between the Y and δ18O signal in garnets.

Ferriphoxite, [(NH4)2K(H2O)][Fe3+(HPO4)2(C2O4)], and carboferriphoxite, [(NH4)K(H2CO3)][Fe3+(HPO4)(H2PO4)(C2O4)], are new mineral species from the Rowley mine, Maricopa County, Arizona, USA. They occur with antipinite, aphthitalite, baryte, fluorite, hematite and quartz in an unusual bat-guano-related, post-mining assemblage. Ferriphoxite occurs as rectangular blades, up to ∼0.1 mm in length, typically forming sprays. Carboferriphoxite occurs as needles or blades, up to ∼0.2 mm in length, typically forming fan- and bowtie-like sprays. Both species are colourless with white streak, vitreous lustre, ∼2 Mohs hardness, brittle tenacity and splintery fracture. Ferriphoxite has three good cleavages ({100}, {010} and {001}) and carboferriphoxite has two good cleavages (probably {100} and {001}). Both species have a measured density of 2.14(2) g·cm–3. Ferriphoxite is biaxial (+) with α = 1.524(3), β = 1.560(3), γ = 1.608(3) and 2Vmeas. = 83.9(4)°. Carboferriphoxite is biaxial (+) with α = 1.525(3), β = 1.555(calc), γ = 1.630(3) and 2Vmeas. = 67(1)°. Electron probe microanalysis gave {[(NH4)2.13K0.87]Σ3.00(H2O)} {(Fe3+0.95Al0.05)Σ1.00(HPO4)2(C2O4)} for ferriphoxite and {[(NH4)1.12K0.88]Σ2.00(H2CO3)} {(Fe3+0.78Al0.22)Σ1.00(HPO4)(H2PO4)(C2O4)} for carboferriphoxite. Ferriphoxite is monoclinic, P21/c, with a = 11.389(5), b = 6.352(3), c = 18.716(9), β = 102.887(9)°, V = 1319.8(11) Å3 and Z = 4. Carboferriphoxite is triclinic, P$\bar 1$, with a = 6.4405(3), b = 9.399(5), c = 11.839(6) Å, α = 95.763(10), β = 92.314(10), γ = 100.665(8)°, V = 695.6(6) Å3 and Z = 2. The structures of ferriphoxite (R1 = 0.0678 for 1850 I > 2σI reflections) and carboferriphoxite (R1 = 0.0427 for 3602 I > 2σI reflections) both contain double-strand chains of corner-sharing Fe3+O6 octahedra and PO3(OH) tetrahedra. The chain in ferriphoxite is decorated by PO3OH tetrahedra and C2O4 groups and that in carboferriphoxite is decorated by PO2(OH)2 tetrahedra and C2O4 groups. The interstitial units in both structures contain K+ and NH4+ cations along with a H2O group in ferriphoxite and an H2CO3 group in carboferriphoxite.

Allanite-(Y), ideally CaY(Al2Fe2+)(Si2O7)(SiO4)O(OH), is a valid species with the type locality in the Åskagen pegmatite, Värmland, Sweden. The mineral occurs as an accessory phase in the blocky zone of the NYF granitic pegmatite near Åskagen, Värmland, Sweden. It forms rims together with iimoriite-(Y), gadolinite-(Y) and allanite-(Nd) around altered crystals of thalénite-(Y). Allanite-(Y) replaced primary thalénite-(Y) during an episode of early post-magmatic hydrothermal activity. Allanite-(Y) forms euhedral crystals with size up to 1 mm, black with a vitreous lustre, conchoidal fracture and greyish brown streak. It has a Mohs hardness of ca. 6, the calculated density of 3.945 g.cm–3 and is biaxial (−) with α = 1.760(3), β = 1.799(2) and γ = 1.784(3) in 589 nm light; pleochroism is weak pale yellowish brown in all directions. Allanite-(Y) has monoclinic symmetry, with the space group P21/m, a = 8.8520(8) Å, b = 5.6959(5) Å, c = 10.0543(9) Å, β = 115.510(2)°, V = 457.52(7) Å3 and Z = 2. Crystal-chemical analysis resulted in the empirical formula: A1(Ca0.900Mn0.090Na0.010)Σ1.000A2(Y0.323Ca0.260Nd0.118Sm0.087Gd0.098Dy0.044Ce0.034Pr0.014Tb0.012Er0.005La0.003Ho0.002Yb0.001)Σ1.001M1(Al0.921Fe2+0.070Ti0.003)Σ0.994M2(Al1.000)M3(Fe2+0.638Fe3+0.262Al0.072Mg0.028)Σ1.000T1(Si1.000)T2(Si1.000)T3(Si1.003)O12.000(OH)1.000.

Allanite-(Y) belongs to the allanite group of the epidote supergroup. The closest end-member compositions of valid allanite group species are allanite-(Ce), allanite-(La) and allanite-(Nd) related via the simple exchange mechanism Y ↔ Ln. The allanite-(Y) origin during metasomatic replacement of the thalénite-(Y) was mainly affected by local system composition and structural constraints rather than Ln+Y fluoride complexation in hydrothermal solution.

The Jabal Radwa pluton (referred to here as the Radwa alkali granite), northwestern Arabian Shield, Kingdom of Saudi Arabia, is a near-circular exposure of peralkaline granite. Previous TIMS U–Pb age determinations of multigrain zircon fractions suggested an age of ∼480 Ma, at least 100 m.y. younger than the youngest known rocks of the Arabian Shield.

A single sample of the Radwa alkali granite contains dark brown, green, blue, tan and yellow colour populations of zircon, plus yellow titanite. The ages of dark brown zircon were unobtainable by SHRIMP due to large matrix effects caused by high concentrations of REE and other trace elements. Green and blue zircon grains were determined to be ∼518 Ma. Tan zircon forms prismatic crystals that resemble those typical of igneous zircon. Three analytical investigations for tan zircon resulted in a SHRIMP age of 501.3 ± 3.9 and LA-ICP-MS ages of 506.7 ± 7.8 and 501.2 ± 5.4 Ma, confirming the uncharacteristically young age of this granite. Yellow zircon yielded a LA-ICP-MS age of 493 ± 13 Ma. Dark brown, green and blue zircon are considered to be xenocrysts, whereas tan and yellow zircon are igneous in origin.

REE distribution patterns define two groups of zircon. Group 1 is composed of tan, yellow and dark brown zircon that have HREE-enriched patterns typical of igneous zircon. Group 2 is composed of green and blue zircon that have essentially horizontal REE patterns typical of hydrothermal zircon.

Because essentially all Proterozoic magmatism in the Arabian Shield ended by ∼570 Ma, magmatism recorded by the Radwa alkali granite might represent igneous activity associated with the Cadomian orogeny and southward subduction beneath the northern edge of Gondwana.