Vibrational spectroscopic characterization of the sulphate mineral leightonite K2Ca2Cu(SO4)4⋅2H2O – Implications for the molecular structure

The mineral leightonite, a rare sulphate mineral of formula K2Ca2Cu(SO4)4.2H2O, has been studied using a combination of electron probe and vibrational spectroscopy. The mineral is characterized by an intense Raman band at 991 cm-1 attributed to the SO2- 4 m1 symmetric stretching mode. A series of Raman bands at 1047, 1120, 1137, 1163 and 1177 cm-1 assigned to the SO2- 4 m3 antisymmetric stretching modes. The observation of multiple bands shows that the symmetry of the sulphate anion is reduced. Multiple Raman\ud and infrared bands in the OH stretching region shows that water in the structure of leightonite is in a range of molecular environments

Strain localization and fluid-assisted deformation in apatite and its influence on trace elements and U–Pb systematics

This paper presents electron backscatter diffraction (EBSD), trace element and U–Pb data of apatite grains from a granitic mylonite from the Taxaquara Shear Zone (SE Brazil). The mylonite recrystallized under upper-greenschist facies and presents two types of apatite with distinct microstructures. Type-1 apatite appears in quartz-rich layers and does not exhibit any microstructural, crystallographic, or chemical evidence of deformation/recrystallization, and resembles the original igneous apatite. Type-2 apatite appears in mica-rich layers and exhibits core-and-mantle microstructures, and intragranular subgrain development, suggesting that they have undergone dynamic recrystallization. Recrystallized tails of type-2 apatite grains exhibit a strong c-axis crystallographic preferred orientation parallel to the X-direction (stretching lineation), and lack evidence of dislocation density. This evidence from type-2 apatite grains, combined with REE depletion, high La and a negative Ce anomaly compared to type-1 grains, suggests that type-2 apatite tails underwent recrystallization via dissolution-precipitation creep, whereas parental grains underwent crystal-plastic deformation and subgrain formation through dynamic recrystallization. Phase-equilibrium modelling and quartz CPO opening-angle thermometry are consistent with recrystallization at ∼480 – 530°C and 2.2 – 5.0 kbar. We were not able to determine precise deformation ages from type-2 apatite because fluid-assisted recrystallization appears to have substantially decreased the U/Pb ratio. We find that preferential fluid flow along high-strain, biotite-rich layers in the mylonite caused type-2 apatite to recrystallise, whereas type-1 apatite in low strain layers was unaffected and retained the characteristics of the protolith

Vibrational spectroscopic characterization of the phosphate mineral phosphophyllite ? Zn2Fe(PO4)2 4H2O, from Hagendorf S?d, Germany and in comparison with other zinc phosphates.

This research was undertaken on phosphophyllite sample from the Hagendorf S?d pegmatite, Bavaria, Germany. Chemical analysis was carried out by Scanning Electron Microscope in the EDS mode and indicates a zinc and iron phosphate with partial substitution of manganese, which partially replaced iron. The calculated chemical formula of the studied sample was determined to be: Zn2(Fe0.65, Mn0.35)P1.00(PO4)2- .4(H2O). The intense Raman peak at 995 cm^-11 is assigned to the m1 PO4^3- symmetric stretching mode and the two Raman bands at 1073 and 1135 cm^-1 to the m3 PO4^3- antisymmetric stretching modes. The m4 PO4^3- bending modes are observed at 505, 571, 592 and 653 cm^-1 and the m2 PO4^3- bending mode at 415 cm^-1. The sharp Raman band at 3567 cm^-1 attributed to the stretching vibration of OH units brings into question the actual formula of phosphophyllite. Vibrational spectroscopy enables an assessment of the molecular structure of phosphophyllite to be assessed