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Modulated photocurrent mapping of electrical micro-junctions related to neighboring p-n zones in single or mixed phase sulphide assemblages can detect galvanic pairs which drive electrochemical reactions with overlaying fluids which is an important process for the petrophysics of geometallurgy. Understanding the role micro-junctions play in retarding or enhancing dissolution of an ore carrying sulphide requires imaging these couples near the surface and correlating them with both phase and elemental distributions. Here we apply multi-modal correlative imaging of a pyrite-sphalerite assemblage involving elemental mapping using electron and proton beam methods followed by laser beam induced current microscopy to reveal the spatial location of internal fields associated with micro-galvanic cells. This represents an important step in advancing electrochemical ore genesis models and further extends the toolkit for understanding and optimising mineral processing schemes based on specific geometallurgical footprints.

Regerite, KFe.sub.6 (PO.sub.4).sub.4 (OH).sub.7 (H.sub.2 O).sub.6 â 4H.sub.2 O, is the first new mineral species to be characterised from the Kreuzberg pegmatite, Pleystein, in the Oberpfalz, Bavaria. It was found in vugs on a specimen of drusy quartz, associated with rockbridgeite, strengite and phosphosiderite. Regerite occurs as clusters of yellowish-green prisms, typically 5 to 20 µm wide and up to 0.1 mm long. The crystals are flattened on 100 and elongated along [001], and they display the forms 100, 010 and 011. The measured density is 2.69(2) g cm.sup.-3 . Optically, regerite crystals are biaxial (+), with α=1.670(5), β=1.690(5) and γ=1.730(5) (measured in white light), and 2V (meas) is 76(2).sup.\" . The empirical formula from electron microprobe analyses and crystal structure refinement is K.sub.0.95 (Fe5.663+Ti.sub.0.45).sub.Σ6.11 (PO.sub.4).sub.3.95 (OH).sub.7 [(H.sub.2 O).sub.5.33 (OH).sub.0.88 ].sub.Σ6.21 â 4H.sub.2 O. Regerite has monoclinic symmetry, with space group P21/c and unit-cell parameters a=15.408(11) Ã, b=17.311(11) Ã, c=9.870(11) Ã, β=95.42(2).sup.\", V=2621(3) Ã.sup.3 and Z=4. The crystal structure was refined using synchrotron single-crystal data to wR.sub.obs =0.065 for 6088 reflections with I3Ï(I). The structure type has not been previously reported. It is made of heteropolyhedral layers parallel to 100 that consist of Fe-centred octahedra and PO.sub.4 tetrahedra. The layers are interconnected via edge-shared octahedral dimers to form slit-like channels along [001] that are occupied by K.sup.+ ions and water molecules.

A single-crystal structure determination and refinement has been conducted for the type specimen of paulkerrite. The structure analysis showed that the mineral has monoclinic symmetry, space group P21/c, not orthorhombic, Pbca, as originally reported. The unit-cell parameters are a=10.569(2), b=20.590(4), c=12.413(2) Å, and β=90.33(3)∘. The results from the structure refinement were combined with electron microprobe analyses to establish the empirical structural formula A1[(H2O)0.98K0.02]Σ1.00 A2K1.00 M1(Mg1.02Mn0.982+)Σ2.00 M2(Fe1.203+Ti0.544+Al0.24Mg0.02)Σ2.00 M3(Ti0.744+ Fe0.263+)Σ1.00 (PO4)4.02 X[O1.21F0.47(OH)0.32]Σ2.00(H2O)10 ⋅ 3.95H2O, which leads to the end-member formula (H2O)KMg2Fe2Ti(PO4)4(OF)(H2O)10 ⋅ 4H2O. A proposal for a paulkerrite group, comprising orthorhombic members benyacarite, mantiennéite, pleysteinite, and hochleitnerite and monoclinic members paulkerrite and rewitzerite, has been approved by the International Mineralogical Association's Commission for New Minerals, Nomenclature and Classification. The general formulae are A2M12M22M3(PO4)4X2(H2O)10 ⋅ 4H2O and A1A2M12M22M3(PO4)4X2(H2O)10 ⋅ 4H2O for orthorhombic and monoclinic species, respectively, where A= K, H2O, □ (= vacancy); M1 = Mn2+, Mg, Fe2+, Zn (rarely Fe3+); M2 and M3 = Fe3+, Al, Ti4+ (and very rarely Mg); X= O, OH, F. In monoclinic species, K and H2O show an ordering at the A1 and A2 sites, whereas O, (OH), and F show a disordering over the two non-equivalent X1 and X2 sites, which were hence merged as X2 in the general formula. In both monoclinic and orthorhombic species, a high degree of mixing of Fe3+, Al, and Ti occurs at the M2 and M3 sites of paulkerrite group members, making it difficult to get unambiguous end-member formulae from the structural determination of the constituents at individual sites. To deal with this problem an approach has been used that involves merging the compositions at the M2 and M3 sites and applying the site-total-charge method. The merged-site approach allows end-member formulae to be obtained directly from the chemical analysis without the need to conduct crystal-structure refinements to obtain the individual site species.

Regerite, KFe6(PO4)4(OH)7(H2O)6 ⋅ 4H2O, is the first new mineral species to be characterised from the Kreuzberg pegmatite, Pleystein, in the Oberpfalz, Bavaria. It was found in vugs on a specimen of drusy quartz, associated with rockbridgeite, strengite and phosphosiderite. Regerite occurs as clusters of yellowish-green prisms, typically 5 to 20 µm wide and up to 0.1 mm long. The crystals are flattened on 100 and elongated along [001], and they display the forms 100, 010 and 011. The measured density is 2.69(2) g cm-3. Optically, regerite crystals are biaxial (+), with α=1.670(5), β=1.690(5) and γ=1.730(5) (measured in white light), and 2V (meas) is 76(2)∘. The empirical formula from electron microprobe analyses and crystal structure refinement is K0.95(Fe5.663+Ti0.45)Σ6.11(PO4)3.95(OH)7[(H2O)5.33(OH)0.88]Σ6.21 ⋅ 4H2O. Regerite has monoclinic symmetry, with space group P21/c and unit-cell parameters a=15.408(11) Å, b=17.311(11) Å, c=9.870(11) Å, β=95.42(2)∘, V=2621(3) Å3 and Z=4. The crystal structure was refined using synchrotron single-crystal data to wRobs=0.065 for 6088 reflections with I>3σ(I). The structure type has not been previously reported. It is made of heteropolyhedral layers parallel to 100 that consist of Fe-centred octahedra and PO4 tetrahedra. The layers are interconnected via edge-shared octahedral dimers to form slit-like channels along [001] that are occupied by K+ ions and water molecules.

Fluor-rewitzerite, [(H.sub.2 O)K]Mn.sub.2 (Al.sub.2 Ti)(PO.sub.4).sub.4 (OF)(H.sub.2 O).sub.10 â4H.sub.2 O, is a new monoclinic member of the paulkerrite group, from the Hagendorf-Süd pegmatite, Oberpfalz (Upper Palatinate in English), Bavaria, Germany. It occurs on the walls of vugs in corroded zwieselite, in association with Zn- and Al-bearing earlshannonite, fluorapatite, jahnsite-(CaMnMn) and Al-rich strunzite. Fluor-rewitzerite forms clusters of colourless stubby prisms up to 0.1 mm long that are flattened on 010; elongated along [100]; and show the forms 100, 010, 001, 111 and 111-. Twinning occurs by 2-fold rotation about c. The measured density is 2.42(2) g cm.sup.-3 . Optically, fluor-rewitzerite crystals are biaxial (+), with α = 1.569(3), β = 1.582(3), γ = 1.602(3) (white light) and 2V(meas) = 78(1)°. The empirical formula from electron microprobe analyses and structure refinement is .sup.A1 [(H.sub.2 O).sub.0.85 K.sub.0.15 ].sub.Σ1.00 .sup.A2 (K.sub.1.00) .sup.M1 (Mn.sup.2+ .sub.1.50 Mg.sub.0.09 Fe.sup.2+ .sub.0.41).sub.Σ2.00 .sup.M2+M3 (Al.sub.1.70 Ti.sup.4+ .sub.0.89 Fe.sup.3+ .sub.0.42).sub.Σ3.01 (PO.sub.4).sub.3.99 .sup.X (O.sub.1.09 F.sub.0.92).sub.Σ2.01 (H.sub.2 O).sub.10 â4.12H.sub.2 O. Fluor-rewitzerite has monoclinic symmetry with space group P2.sub.1 /c and unit-cell parameters a = 10.407(1) Ã, b = 20.514(2) Ã, c = 12.193(1) Ã, β = 90.49(2)°, V = 2603.0(4) Ã.sup.3 and Z = 4. The crystal structure was refined using synchrotron single-crystal data to R.sub.obs =0.058 for 6186 reflections with I3Ï(I). Fluor-rewitzerite is the fluoride analogue of rewitzerite, with F dominant over OH at the X sites of the general formula A1A2M1.sub.2 M2.sub.2 M3(PO.sub.4).sub.4 X.sub.2 (H.sub.2 O).sub.10 â4H.sub.2 O.

Fluor-rewitzerite, [(H2O)K]Mn2(Al2Ti)(PO4)4(OF)(H2O)10⋅4H2O, is a new monoclinic member of the paulkerrite group, from the Hagendorf-Süd pegmatite, Oberpfalz (Upper Palatinate in English), Bavaria, Germany. It occurs on the walls of vugs in corroded zwieselite, in association with Zn- and Al-bearing earlshannonite, fluorapatite, jahnsite-(CaMnMn) and Al-rich strunzite. Fluor-rewitzerite forms clusters of colourless stubby prisms up to 0.1 mm long that are flattened on 010; elongated along [100]; and show the forms 100, 010, 001, 111 and 111‾. Twinning occurs by 2-fold rotation about c. The measured density is 2.42(2) g cm-3. Optically, fluor-rewitzerite crystals are biaxial (+), with α = 1.569(3), β = 1.582(3), γ = 1.602(3) (white light) and 2V(meas) = 78(1)°. The empirical formula from electron microprobe analyses and structure refinement is A1[(H2O)0.85K0.15]Σ1.00A2(K1.00) M1(Mn2+1.50Mg0.09Fe2+0.41)Σ2.00M2+M3(Al1.70Ti4+0.89Fe3+0.42)Σ3.01(PO4)3.99X(O1.09F0.92)Σ2.01(H2O)10⋅4.12H2O. Fluor-rewitzerite has monoclinic symmetry with space group P21/c and unit-cell parameters a = 10.407(1) Å, b = 20.514(2) Å, c = 12.193(1) Å, β = 90.49(2)°, V = 2603.0(4) Å3 and Z = 4. The crystal structure was refined using synchrotron single-crystal data to Robs=0.058 for 6186 reflections with I>3σ(I). Fluor-rewitzerite is the fluoride analogue of rewitzerite, with F dominant over OH at the X sites of the general formula A1A2M12M22M3(PO4)4X2(H2O)10⋅4H2O.

Hydroxylbenyacarite, (H2O)2Mn2(Ti2Fe) (PO4)4 [O(OH)] (H2O)10·4H2O, is a new paulkerrite-group mineral from the El Criollo mine, Cordoba Province, Argentina (IMA2023-079). It was found in specimens of altered triplite, in association with bermanite, phosphosiderite, quartz, strengite and manganese oxides. Hydroxylbenyacarite occurs as light greenish-yellow rhombic tablets with dimensions of typically 20 to 50 µm, occasionally to 400 µm. The crystals are flattened on {010}, slightly elongated on [001] and bounded by the {111} and {010} forms. The calculated density is 2.32 g cm-3. Optically, hydroxylbenyacarite crystals are biaxial (+), with α=1.608(3), β=1.624(3), γ=1.642(3) (measured in white light) and 2V(meas.)=88(2)°. The calculated 2V is 87.5°. The empirical formula is Ca0.06A[K0.46(H2O)0.88[]0.66]Σ2.00 M1(Mn1.52Mg0.02Fe2+0.35[]0.11)Σ2.00 M2+M3(Fe3+1.21Al0.02Ti1.77)Σ3.00(PO4)4 X[F0.16(OH X[F0.16(OH)0.70O1.14]Σ2.00(H2O)10·3.77H2O. The average crystal structure for hydroxylbenyacarite has space group Pbca and unit cell parameters a=10.5500(3) Å, b=20.7248(5) Å, c=12.5023(3) Å, V=2733.58(12) Å3 and Z=4. It was refined using single-crystal data to wRobs=0.074 for 2611 reflections with I>3σ(I). The crystal structure contains corner-connected linear trimers of Ti-centred octahedra that share corners with PO4 tetrahedra to form 10-member rings parallel to (010). K+ cations and water molecules are located in interstitial sites within the rings. Additional corner-sharing of the PO4 tetrahedra with MnO2(H2O)4 octahedra occurs along [010] to complete the 3D framework structure. A new eight-coordinated interstitial site, previously unreported for paulkerrite-group minerals, is occupied by Ca2+ cations. Weak diffuse diffraction spots in reconstructed precession images for hydroxylbenyacarite violate the a and b glide plane extinctions for Pbca and are consistent with local, unit-cell-scale regions of monoclinic, P21/c structure, in which ordering of the interstitial K+ and Ca2+ cations occurs.

Rewitzerite, K(H2O)Mn2(Al2Ti)(PO4)4[O(OH)](H2O)10·4H2O, is a new monoclinic member of the paulkerrite group, from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany. It was found in specimens of altered zwieselite, in association with rockbridgeite. Rewitzerite forms clusters of colourless elongated hexagonal-shaped prisms, up to 0.1 mm long. The crystals are flattened on {010} and elongated along [100], with forms {010}, {001}, {111} and {1̄11}. The calculated density is 2.33 g·cm-3. Optically, rewitzerite crystals are biaxial (+), with α = 1.585(2), β = 1.586(2), γ = 1.615(2) (measured in white light) and 2V(meas) = 25(2)°. The empirical formula from electron microprobe analyses and structure refinement is A1[K0.77(H2O)0.23]A2[H2O] M1(Mn2+0.82Mg0.64Fe3+0.43∎0.11)Σ2.00M2+M3(Al1.51Ti4+1.06F e3+0.43)Σ3.00(PO4)4X[(OH)0.54F0.42O1.04]Σ2.00(H2O)10·4H2O, where ∎ = vacancy. Rewitzerite has monoclinic symmetry with space group P21/c and unit-cell parameters a = 10.444(2) Å, b = 20.445(2) Å, c = 12.2690(10) Å, β = 90.17(3)°, V = 2619.8(6) Å3 and Z = 4. The crystal structure was refined using synchrotron single-crystal data to wRobs = 0.068 for 5894 reflections with I > 3σ(I). The crystal structure has the same topology as that for orthorhombic paulkerrite-group minerals but differs primarily in having an ordering of K+ and H2O molecules in different A sites, whereas they are disordered at a single A site in the orthorhombic members of the group.

Dental caries, erosion and hypersensitivity are major public health problems. SnF 2 is used widely in oral care products to help prevent/treat these conditions. Casein phosphopeptide-stabilised amorphous calcium phosphate nanocomplexes (CPP-ACP) are a biomimetic nanotechnology of salivary phosphopeptide-ACP complexes that deliver bioavailable calcium and phosphate ions to promote dental remineralisation (repair). We show here using in vitro studies and a double-blind, randomised controlled, cross-over design in situ clinical trial that SnF 2 and CPP-ACP interact to form a nanofilament coating on the tooth surface and that together they are superior in their ability to promote dental remineralisation. Sn(II) by cross-linking the CPP-ACP helps to stabilise the complexes which improves delivery to the tooth surface and enhances binding and ion incorporation into tooth mineral. The combination of SnF 2 and CPP-ACP in oral care products may significantly improve their efficacy in prevention/treatment of dental caries/erosion and hypersensitivity.