Kyanoxalite,a new cancrinite-group mineral species with extraframework oxalate anion from the Lovozero alkaline pluton,Kola Peninsula

Kyanoxalite, a new member of the cancrinite group, has been identified in hydrothermally altered hyperalkaline rocks and pegmatites of the Lovozero alkaline pluton, Kola Peninsula, Russia. It was found at Mount Karnasurt (holotype) in association with nepheline, aegirine, sodalite, nosean, albite, lomonosovite, murmanite, fluorapatite, loparite, and natrolite and at Mt. Alluaiv. Kyanoxalite is transparent, ranging in color from bright light blue, greenish light blue and grayish light blue to colorless. The new mineral is brittle, with a perfect cleavage parallel to (100). Mohs hardness is 5–5.5. The measured and calculated densitiesare 2.30(1) and 2.327 g/cm³, respectively. Kyanoxalite is uniaxial, negative, ω = 1.794(1), ɛ = 1.491(1). It is pleochroic from colorless along E to light blue along O. The IR spectrum indicates the presence of oxalate anions C₂O₄²⁻ and water molecules in the absence of CO₃²⁻ Oxalate ions are confirmed by anion chromatography. The chemical composition (electron microprobe; water was determined by a modified Penfield method and carbon was determined by selective sorption from annealing products) is as follows, wt %: 19.70 Na₂O, 1.92 K₂O, 0.17 CaO, 27.41 Al₂O₃, 38.68 SiO₂, 0.64 P₂O₅, 1.05 SO₃, 3.23 C₂O₃, 8.42 H₂O; the total is 101.18. The empirical formula (Z = 1) is (Na_6.45K_0.41Ca_0.03)_Σ6.89(Si_6.53Al_5.46O₂₄)[(C₂O₄)_0.455(SO₄)_0.13(PO₄)_0.09(OH)_0.01]_Σ0.68 · 4.74H₂O. The idealized formula is Na₇(Al₅₋₆Si₆₋₇O₂₄)(C₂O₄)_0.5−1 · 5H₂O. Kyanoxalite is hexagonal, the space group is P6₃, a = 12.744(8), c = 5.213(6) -ray powder diffraction pattern are as follows, [d, [A] (I, %)(hkl)]: 6.39(44) (110), 4.73 (92) (101), 3.679 (72) (300), 3.264 (100) (211, 121), 2.760 (29) (400), 2.618 (36) (002), 2.216, (29) (302, 330). According to the X-ray single crystal study (R = 0.033), two independent C₂O₄ groups statistically occupy the sites on the axis 6₃. The new mineral is the first natural silicate with an additional organic anion and is the most hydrated member of the cancrinite group. Its name reflects the color (κɛανgoΣς is light blue in Greek) and the species-forming role of oxalate anions. The holotype is deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, registration no. 3735/1.     

A Novel Solid Solution between Wagnerite and Arsenowagnerite

Doklady Earth Sciences - A novel solid solution between isostructural Mg arsenate and phosphate of the wagnerite group and a new As5+-rich variety of wagnerite were discovered in sublimates of the...     

Lazurite: Validation as a Mineral Species with the Formula Na7Ca(Al6Si6O24)(SO4) $${\text{S}}_{3}^{{\bullet - }}$$ ⋅H2O and New Data

Geology of Ore Deposits - The status of lazurite as a valid mineral species has been confirmed. The neotype specimen from the Malaya Bystraya gem lazurite deposit, Baikal Lake area has been studied...     

Tourmaline in the Vetka porphyry copper-molybdenum deposit of the Chukchi Peninsula of Russia

Three generations of tourmaline have been identified in propylite in the Vetka porphyry copper-molybdenum deposit of the Chukchi Peninsula of Russia. Tourmaline-I is characterized by its Fe_tot/(Fe_tot + Mg) value, which ranges from 0.33 to 0.49. Tourmaline-II, which crystallizes at a lower temperature, overgrowing tourmaline-I or occurring as isolated crystals, is distinguished by a higher Fe_tot/(Fe_tot + Mg), which varies from 0.46 to 0.72. The Fe_tot/(Fe_tot + Mg) ratio in tourmaline-III, which overgrows tourmaline-II is lower (0.35–0.49), and is identical to that of the first tourmaline generation. This is probably caused by the beginning of sulfide deposition. Tourmalines in the deposit characterized by complex isomorphic substitutions can be attributed to the intermediate members of the dravite—“hydroxy-uvite”-“oxy-uvite” and schorl-“hydroxy-feruvite”-“oxy-feruvite” series. Tourmaline starts to crystallize at temperatures above 340°C. The fluid responsible for the tourmaline deposition was magmatic, with a significant admixture of meteoric water (δ¹⁸O_{H 2}O = −0.85 to −0.75‰). The high Fe³⁺/Fe_tot ratio (0.50) indicates high oxygen activity when the tourmaline precipitated. It has been established that the isomorphic substitution Fe_tot → Al is typomorphic of tourmalines from porphyry copper deposits worldwide.     

Tourmaline from deposits of the Birgil’da-Tomino ore cluster, South Urals

Tourmalines from the Kalinovka porphyry copper deposit with epithermal bismuth-gold-basemetal mineralization and the Michurino gold-silver-base-metal prospect have been studied in the South Urals. Tourmaline from the Kalinovka deposit occurs as pockets and veinlets in quartz-sericite metasomatic rock and propylite. The early schorl-“oxy-schorl” [Fe_tot/(Fe_tot + Mg) = 0.66?0.81] enriched in Fe³⁺ is characterized by the homovalent isomorphic substitution of Fe³⁺ for Al typical of propylites at porphyry copper deposits. The overgrowing tourmalines of the second and third generations from propylite and quartz-sericite metasomatic rock are intermediate members of the dravite-magnesio-foitite solid solution series [Fe_tot/(Fe_tot + Mg) = 0.05?0.46] with homovalent substitution of Mg for Fe²⁺ and coupled substitution of ^X _? + ^YAl for ^XNa + ^YMg. These substitutions differ from the coupled substitution of ^YAl + ^WO^2? for ^YFe²⁺ + ^WOH^? in tourmaline from quartz-sericite rocks at porphyry copper deposits. At the Michurino prospect, the tourmaline hosted in the chlorite-pyrite-quartz veins and veinlets with Ag-Au-Cu-Pb-Zn mineralization is an intermediate member of the dravite-magnesio-foitite solid solution series [Fe_tot/(Fe_tot + Mg) = 0.20?0.31] with homovalent substitution of Mg for Fe²⁺ and coupled substitutions of ^X _? + ^YAl for ^XNa + ^YMg identical to that of late tourmaline at the Kalinovka deposit. Thus, tourmalines of the porphyry and epithermal stages are different in isomorphic substitutions, which allow us to consider tourmaline as an indicator of super- or juxtaposed mineralization.     

Calorimetric Study of Natural Basic Copper Phosphate—Pseudomalachite

The thermochemical study of a natural basic copper phosphate, pseudomalachite Cu₅(PO₄)₂(OH)₄ (Virneberg deposit, Germany), was carried out using high-temperature melt solution calorimetry method with a Tian–Calvet microcalorimeter. The enthalpy of formation of the mineral from elements was obtained to be Δ _f H_el(298.15 K) =–3214 ± 13 kJ/mol. The value of the Gibbs energy of pseudomalachite formation calculated using literature data on its standard entropy is Δ _f H_el^°(298.15 K) =–2812 ± 13 kJ/mol.     

Cancrinite and cancrisilite in the Khibina-Lovozero alkaline complex: Thermochemical and thermal data

The paper presents the results of a thermochemical and thermal study of cancrinite, (Na_6.93Ca_0.545K_0.01)_Σ7.485[(Si_6.47Al_5.48Fe_0.05)_Σ12O₂₄](CO₃)_1.25 · 2.30 H₂O, and cancrisilite, (Na_7.17 Ca_0.01)_Σ7.18[(Si_7.26Al_4.70Fe_0.04)_Σ12O₂₄][(CO₃)_1.05(OH)_0.21(PO₄)_0.04(SO₄)_0.01] · 2.635 H₂O, from the Khibina-Lovozero Complex, Kola Peninsula, Russia. Stages of the thermal decomposition of these minerals were studied using IR spectroscopy. The enthalpies of formation of the minerals from elements were determined by melt drop solution calorimetry: Δ _f H _el ⁰ (298.15 K) = ?14 490 ± 16 kJ/mol for cancrinite and ?14302 ± 17 kJ/mol for cancrisilite. The values of Δ _f H _el ⁰ (298.15 K), S ^o(298.15 K), and Δ _f H _el ⁰ (298.15 K) are determined for cancrinite and cancrisilite of theoretical composition.