Two sodalite samples (sample I is Na₈Al₆Si₆O₂₄Cl₂⋅0.4H₂O from the Kovdor alkaline ultramafic massif with carbonatites in the Murmansk region, Russia, and sample II is Na₈Al₆Si₆O₂₄Cl₂⋅0.2H₂O from the Bayan Kol nepheline syenite and miaskite massif in the Republic of Tyva) were studied by thermal and electron-microprobe analyses, powder X-ray diffraction, photoluminescence, and by IR, Raman, and ESR spectroscopy. Solution melt calorimetry was applied to determine the enthalpy of formation from elements for water-bearing sodalite samples: −13536 ± 10 (I) and −13503 ± 19 (II) kJ/mol. The enthalpy of formation of sodalite of the theoretical composition Na₈Al₆Si₆O₂₄Cl₂ was evaluated at Δ_fH⁰(298.15 K) = −13446 ± 11 kJ/mol. The data obtained on the enthalpy of formation of sodalite and literature data on its S⁰(298.15 K) were used to calculate the standard Gibbs energies of formation of anhydrous and of water-bearing sodalite.

The new eudialyte-group mineral, odikhinchaite, was discovered in a peralkaline pegmatite vein hosted by melteigite at the Odikhincha ultrabasic alkaline–carbonatite intrusion, Taimyr Peninsula, Krasnoyarsk Krai, Russia. Associated minerals are orthoclase, albite, aegirine, cancrinite, ancylite-(Ce), catapleiite, and wadeite. Odikhinchaite occurs as dense rosette-like aggregates up to 11 mm across, consisting of split lamellar individuals. The mineral is translucent to transparent, deep purple, with vitreous luster. Odikhinchaite is brittle, with uneven fracture; distinct cleavage on (001) is observed. Hardness determined by the micro-indentation method is equal to 430 kgf/mm²; the Mohs hardness is 5. D(meas.) is 2.97(1) g·cm⁻³, D(calc.) is 3.04 g·cm^–3. Odikhinchaite is optically uniaxial (–), ω = 1.638(2), ε = 1.630(2). The IR spectrum shows the presence of the ^IVMn²⁺O₄ polyhedra, H₂O molecules and CO₃^2– anions. The chemical composition is (electron microprobe, H₂O determined by the modified Penfield method, CO₂ determined by selection sorption of gaseous annealing products; wt%): Na₂O 9.25, K₂O 0.59, CaO 12.77, MnO 5.49, FeO 0.75, MgO 0.24, La₂O₃ 0.38, Ce₂O₃ 0.39, Nd₂O₃ 0.15, Al₂O₃ 0.07, SiO₂ 44.80, ZrO₂ 11.13, TiO₂ 0.07, Nb₂O₅ 4.17, Cl 0.69, CO₂ 0.90, H₂O 2.22, –O = Cl –0.16, total 99.72. The crystal structure was solved using single-crystal X-ray diffraction data. Odikhinchaite is trigonal, space group R3m; the unit-cell parameters are: a = 14.2837(2) Å, c = 30.0697(3) Å, V = 5313.04(12) ų. The new mineral is isostructural with other 12-layered members of the eudialyte group with the space group R3m. Its crystal chemical formula is (Z = 3): {^N1(Na_2.58Ca_0.42)^N2[Na_2.37Ca_0.51(H₂O)_0.12]^N3(Sr_2.00K_0.45Na_0.35REE_0.20)^N4Na₃^N5[(H₂O)_1.8Na_1.2]}{^ZZr₃^M1Ca₆^M2(Mn_2.49Fe²⁺_0.51)[^M3Nb(OH)_1.82O_1.18](^M4SiOH)[Si₃O₉]₂[Si₉O₂₇]₂^X1[(CO₃)_0.53Cl_0.47]^X2[(H₂O)_0.6(O,F)_0.4]^XM4(CO₃)_0.15. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 11.42 (64) (101), 4.309 (41) (205), 3.405 (53) (131), 3.208 (45) (208, 036), 3.167 (44) (217), 2.978 (100) (315), 2.858 (86) (404).

Coquimbite Al\({\text{Fe}}_{3}^{{3 + }}\)[SO₄]₆(H₂O)₁₂⋅6H₂O (sample from the Javier Mine, Peru) has been studied by thermal and electron microprobe analysis, X-ray powder diffraction, Raman spectroscopy, and Mössbauer spectroscopy. The enthalpy of formation of the coquimbite from elements ∆_fH⁰(298.15 K) = −11 118 ± 40 kJ/mol was determined by the method of solution calorimetry in melt of lead borate 2PbO∙B₂O₃ on a Setaram (France) Calvet microcalorimeter. The value of its absolute entropy S⁰(298.15 K) = 1248.3 ± 3.0 J/(mol K) was estimated, the entropy of formation ∆_fS⁰(298.15 K) = − 5714.0 ±3.0 J/mol K), and the Gibbs energy of formation from elements ∆_fG⁰(298.15 K) = −9411 ± 40 kJ/mol were calculated. The values of the enthalpy and Gibbs energy of formation of aluminocoquimbite Al₂\({\text{Fe}}_{2}^{{3 + }}\)[SO₄]₆(H₂O)₁₂⋅6H₂O from elements were estimated at −11 540 ± 29 and −9830 ± 29 kJ/mol, respectively.

Brazilianite Na_0.91Al_3.03(PO₄)_1.98(OH)_4.06 (Galilea, Minas Gerais, Brazil) has been studied by thermal and electron microprobe analysis, powder X-ray diffraction, IR, Raman, and EPR spectroscopy. The EPR method has established that the peculiar feature of the studied sample is the presence of a structural impurity of vanadium. The enthalpy of formation of brazilianite NaAl₃(PO₄)₂(OH)₄ from the elements ∆_fH⁰(298.15 K) = −5322.3 ± 5.1 kJ/mol was determined by the method of calorimetry of dissolution in a melt of lead borate 2PbO∙B₂O₃ on a Setaram (France) Calvet microcalorimeter. The value of the absolute entropy S⁰(298.15 K) = 303.8 ± 0.9 J/(mol K) was estimated, and the entropy of formation ∆_fS⁰(298.15 K) = − 1407.1 ± 1.1 J/(mol K) and the Gibbs energy of formation from elements ∆_fG⁰(298.15 K) = − 4902.8 ± 5.1 kJ/mol were calculated.

The paper reports the first comprehensive physicochemical study of minerals of the amblygonite LiAlPO₄F–montebrasite LiAlPO₄(OH) series. An EPR spectroscopic and calorimetric study of montebrasite LiAlPO₄(OH)_0.9F_0.1 from the Shuk-Byul rare-metal granite pegmatites (Sangilen Highlands, Tuva) and amblygonite LiAlPO₄F_0.5(OH)_0.5 from pegmatites of the Voron’i Tundras (Kola Peninsula) was carried out. Using the EPR method, the radiation-sensitive paramagnetic O^– centers were discovered. They were formed without participation of impurity elements in the regular sites of crystal lattice. The possibility use of minerals of the amblygonite–montebrasite series for EPR geochronometry has been demonstrated for the first time. Using the method of high-temperature melt dissolution calorimetry on a Tian-Calvét microcalorimeter, the enthalpies of formation from elements \({{\Delta }_{f}}H_{{{\text{el}}}}^{0}\) (298.15 K) = –2326.3 ± 2.2 kJ/mol for montebrasite with the composition LiAl(PO₄)(OH)_0.9F_0.1 and for amblygonite with the composition LiAl(PO₄)F_0.5(OH)_0.5 (‒2347.9 ± 3.1 kJ/mol) are obtained; and the values of this parameter are calculated for the end members with an ideal composition of the series: for montebrasite (–2315.5 ± 2.2 kJ/mol) and for amblygonite (–2401.6 ± 3.1 kJ/mol). The values of the standard entropy S⁰ (298.15 K) and the Gibbs energy of formation \({{\Delta }_{f}}G_{{{\text{el}}}}^{0}\) (298.15 K) for intermediate and end members of the amblygonite–montebrasite series are estimated.

Atacamite, empirical formula (Cu_1.97Zn_0.01)Cl_0.94(OH)_3.02, from the paleofumaroles of the monogenic volcano of Mount 1004, Tolbachik, Kamchatka, Russia, has been studied by thermal and electron microprobe analyses, X-ray powder diffraction, IR and Raman spectroscopy, and Calvet microcalorimetry. The thermal decomposition of atacamite was studied using X-ray diffraction and IR spectroscopy. The enthalpy of formation from elements for atacamite of the theoretical composition Cu₂Cl(OH)₃ (−810.2 ± 7.7 kJ/mol) was determined by melt dissolution calorimetry, and the Gibbs energy of formation (−657.0 ± 7.7 kJ/mol) was calculated. The stability of atacamite in the Cu–O–Cl–H system was thermodynamically modeled based on the obtained data, and the boundaries of its stability field were calculated under conditions of high alkalinity and high acidity of the mineral-forming medium.