Abstract A new member of the rare-earth magnesium pentaborate family, DyMgB 5 O 10 , was synthesized via solid-state reaction followed by flux growth in a K 2 Mo 3 O 10 melt. Single crystals up to 0.5 mm were obtained and characterized by SEM, EDX, DSC, and XRD techniques. The crystal structure was refined in the monoclinic space group P 2 1 / n , confirming that it belongs to the same structural family as other R MgB 5 O 10 compounds. The structure consists of alternating anionic borate layers built from [B 5 O 12 ] 3− clusters and cationic Dy–O–Mg layers. Dy 3+ ions are coordinated by ten oxygen atoms in distorted polyhedra, while Mg 2+ occupy edge-sharing octahedral dimers. Thermal analysis revealed incongruent melting with T onset ∼ 1,072 °C. DFT calculations gave an indirect band gap of ∼6.06 eV, indicating a wide-bandgap dielectric. Photoluminescence and X-ray induced luminescence spectra exhibit characteristic Dy 3+ intra-4 f transitions, with dominant blue ( 4 F 9 / 2 → 6 H 15 / 2 ) and yellow ( 4 F 9 / 2 → 6 H 13 / 2 ) emissions. The intense yellow emission reflects the low symmetry of the DyO 10 polyhedra. Characteristic luminescence under X-ray excitation confirms effective energy transfer from the borate matrix to Dy 3+ . The combination of high thermal stability, wide band gap, and favorable optical properties makes DyMgB 5 O 10 a promising candidate for phosphors and X-ray scintillators.

In most cases, columbite-supergroup minerals are characterized by partial ordering of cations, which makes their identification based only on chemical composition and powder diffraction data difficult. Columbite-supergroup minerals with partially ordered cations were studied by means of electron microprobe analyses, powder and single-crystal X-ray diffraction, including crystal structure refinement in ixiolite-type and wolframine-type models. The samples originate from the Sakhanaiskiy granite massif, Eastern Siberia, Russia, (Sample 1) and from the Heftetjern pegmatite, Telemark, Norway (Sample 2). Their representative empirical formulae are (Fe2+0.81Mn2+0.53)Sigma 1.34Fe3+0.07(Ti0.23Zr0.11Sn0.02)Sigma 0.36(Nb1.45Ta0.26)Sigma 1.71W0.52O8 (Sample 1) and (Mn2+0.28Fe2+0.25)Sigma 0.53Sc1.08(Sn0.32Ti0.04)Sigma 0.36(Ta1.41Nb0.52)Sigma 1.93W0.10O8 (Sample 2). Based on these data and the results of the crystal structure refinement, the studied samples can be considered as columbite-supergroup minerals in which cations are partially ordered in accordance with the wolframite mechanism. An approach is suggested according to which the degree of cation ordering in such columbite-supergroup minerals can be estimated based on the electron contents refined for different sites in a monoclinic model. According to this criterion, the degree of cation ordering of Samples 1 and 2 is 91% and 26%, respectively. Despite a significant degree of cation disordering, transition from the wolframite to ixiolite model results in a significant enhancement of the R-factor of the structure refinement (from 0.0365 to 0.0764 and from 0.0207 to 0.0610, respectively).

Synthetic alumosilicates are used in many industrial applications, and the synthesis of clay minerals under different conditions allows us to understand the conditions of their formation. This study examined the impact of varying silica precursors, pH conditions and synthesis durations. Synthetic kaolinite group mineral analogues were investigated by X-ray diffraction, scanning electron microscopy and infrared spectroscopy. Additionally, the crystallinity index was calculated. The impact of using different silica sources on the structural features of synthetic kaolinite group analogues was revealed. The use of a Nanosil precursor resulted in the formation of highly crystalline kaolinite. The most significant alterations in the course of synthesis were observed at different pH values. The formation of various synthetic analogues of minerals from the kaolinite group was observed: at a high pH, the formation of halloysite with a small admixture of kaolinite was observed. Conversely, the synthesis resulted in the formation of ordered kaolinite at a low pH. The crystallinity index of the resulting synthesized kaolinite analogues rises as the synthesis duration increases, while the quantity of non-crystallized material decreases. The changes in the crystallinity of kaolinite when using different silica precursors are related to the different homogenization of the material that occurs at the stage of alumosilica gel formation.

The new mineral natromolybdite, ideally Na2MoO42H2O, was found in the Arsenatnaya fumarole, Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. The associated minerals are halite, sylvite, aphthitalite, belomarinaite, powellite, hematite, sanidine, tilasite, johillerite, bradaczekite, badalovite, arsmirandite, wrightite, arsenatrotitanite, dmisokolovite, litidionite, rutile and cristobalite. Natromolybdite occurs as rectangular, octagonal or rhomb-like lamellar to thin-tabular crystals up to 40 mu m across and up to 3 mu m thick, in near-parallel, pile-like or rose-like aggregates and crystal crusts up to 0.2 mm across. It is transparent and colourless, with vitreous lustre. Dcalc is 2.573 g/cm3. The synthetic analogue of natromolybdite is optically biaxial (+), alpha = 1.575(2), beta = 1.576(2), gamma = 1.598(3) and 2Vmeas = 20(10)degrees. The chemical composition (wt.%, electron microprobe, H2O is calculated by stoichiometry) is: Na2O 25.51, K2O 0.66, SO3 1.04, MoO3 58.21, H2Ocalc 15.05, total 100.47. The empirical formula, calculated based on O = 6 apfu, is (Na1.971K0.034)Sigma 2.005(Mo0.968S0.031)Sigma 0.999O42H2O. Natromolybdite is orthorhombic, space group Pbca, a = 8.483(1), b = 10.577(2), c = 13.842(2) & Aring;, V = 1242.0(2) & Aring;3 and Z = 8. The nine strongest reflections of the powder XRD pattern [d,& Aring;(I)(hkl)] are: 6.92(100)(002), 4.243(20)(200), 4.206(32)(022), 3.618(31)(202), 3.310(31)(220), 3.169(49)(131), 3.067(21)(114), 2.987(30)(222) and 2.681(15)(204, 311). Natromolybdite (IMA-accepted symbol Nmyb) is named for the chemical composition. It is a natural analogue of a well-studied synthetic sodium molybdate dihydrate.

New niobium lithium 1M mica germanate-silicate KNb(Li0.9Nb0.02 square 0.08)2[(Ge0.4Si0.6)4O10]O2 was synthesized hydrothermally at temperature 280-290 degrees C and a pressure 80-100 atm. It crystallises in the polar C2 space group. The simultaneous inclusion of lithium and niobium was achieved for the first time in the structure, and the presence of octahedral lithium was confirmed by Raman spectroscopy. The trioctahedral central layer possesses one octahedron fully occupied by Nb and two octahedra statistically occupied predominantly by Li with a small Nb impurity and vacancy. Ge-Si isomorphic substitution was revealed in tetrahedra, which made it possible to implement the inclusion of large Nb in the structure compared to conventional micas. The presence of disordered octahedral positions and isomorphism indicates structural defects overall. Between 1M, 2M, 2O, and 3T polytypes in the mica family, topology-symmetry analysis allowed us to find the origin of existence of the 1M or 2M (2O) polytypes based on the symmetry of heteropolyhedral octahedra and tetrahedra packets and symmetry operation of their multiplication in the structures. Under Nd:YAG laser illumination, powders of polar Nb-mica demonstrate second harmonic generation (SHG) with output as high as 20 compared to alpha-quartz powder but only 0.1 to LiNbO3. Despite lower Nb concentration in lithium niobium 1M mica germanate-silicate, the structure-property relation here is similar to LiNbO3, being determined by shortened bonds in the distorted Nb-O octahedron directed along the polar axis.

New Li,Nb–mica 1M structure KNb(Li 0.9 Nb 0.02 □ 0.08 ) 2 [(Ge 0.4 Si 0.6 ) 4 O 10 ]O 2 .

A multimethodic approach based on infrared, Raman, electron spin resonance and photoluminescence spectroscopy, absorption spectroscopy in near infrared, visible and ultraviolet regions, single-crystal X-ray diffraction as well as electron microprobe analyses was applied to the characterization of a new commensurately modulated cubic haüyne analogue with the modulation parameter of 0.2 and unit-cell parameter of 45.3629(3) Å (designated as haüyne-45Å) from the Malobystrinskoe lazurite deposit, in the Baikal Lake area, Siberia, Russia, as well as associated SO32−-bearing afghanite. Haüyne-45Å is the second member, after vladimirivanovite, of the sodalite group with a commensurately modulated structure. The average structure is based on the tetrahedral aluminosilicate sodalite-type framework with sodalite cages of different sizes. The simplified formula of haüyne-45Å is Na6Ca2−x(Si6Al6O24)(SO42−,HS−,S2●−,S4,S3●−,S52−)2−y. The structural modulations of the haüyne-45Å framework are presumably related to the regular alternation of SO42− anions with polysulfide S2●−, S3●−, S4, and S52− groups detected by the spectroscopic methods. Mechanisms of thermal conversions of S-bearing groups in haüyne-45Å under oxidizing and reducing conditions at temperatures up to 800 °C are studied, and their geochemical importance is discussed.

The new mineral natromolybdite, ideally Na2MoO4·2H2O, was found in the Arsenatnaya fumarole, Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. The associated minerals are halite, sylvite, aphthitalite, belomarinaite, powellite, hematite, sanidine, tilasite, johillerite, bradaczekite, badalovite, arsmirandite, wrightite, arsenatrotitanite, dmisokolovite, litidionite, rutile and cristobalite. Natromolybdite occurs as rectangular, octagonal or rhomb-like lamellar to thin-tabular crystals up to 40 μm across and up to 3 μm thick, in near-parallel, pile-like or rose-like aggregates and crystal crusts up to 0.2 mm across. It is transparent and colourless, with vitreous lustre. Dcalc is 2.573 g/cm3. The synthetic analogue of natromolybdite is optically biaxial (+), α = 1.575(2), β = 1.576(2), γ = 1.598(3) and 2Vmeas = 20(10)°. The chemical composition (wt.%, electron microprobe, H2O is calculated by stoichiometry) is: Na2O 25.51, K2O 0.66, SO3 1.04, MoO3 58.21, H2Ocalc 15.05, total 100.47. The empirical formula, calculated based on O = 6 apfu, is (Na1.971K0.034)Σ2.005(Mo0.968S0.031)Σ0.999O4·2H2O. Natromolybdite is orthorhombic, space group Pbca, a = 8.483(1), b = 10.577(2), c = 13.842(2) Å, V = 1242.0(2) Å3 and Z = 8. The nine strongest reflections of the powder XRD pattern [d,Å(I)(hkl)] are: 6.92(100)(002), 4.243(20)(200), 4.206(32)(022), 3.618(31)(202), 3.310(31)(220), 3.169(49)(131), 3.067(21)(114), 2.987(30)(222) and 2.681(15)(204, 311). Natromolybdite (IMA-accepted symbol Nmyb) is named for the chemical composition. It is a natural analogue of a well-studied synthetic sodium molybdate dihydrate.

Pseudobrookite from the Arsenatnaya and Yadovitaya active volcanic fumaroles (Tolbachik volcanic complex, Kamchatka) is characterized for the first time. The chemical composition and peculiarities of isomorphism of minerals of the pseudobrookite group of various genetic groups are studied on the basis of 203 analyses of 40 samples and published literature data on 44 geological objects. It is shown that the subsurface conditions are most favorable for the crystallization of pseudobrookite including that with the composition close to end-member Fe_2^3 + TiO_5 ; lunar rocks contain minerals of the ferropseudobrookite Fe2+Ti2O5–armalcolite MgTi2O5 series characterized by an intermediate Fe2+/Mg ratio, a maximum Ti content, and the absence of Fe3+; and the impact minerals and their technogenic analogs are close in composition to Fe2+Ti2O5. The Tolbachik fumarolic pseudobrookite has a high Al2O3 content (up to 7.1 wt

The crystal structure of the highly hydrous analogue of the K-rich gismondine-Sr from Bellerberg paleovolcano, Eifel Mountains, Germany, was studied by single-crystal X-ray diffraction. Electron microprobe analyses (energy-dispersive spectroscopy analyses) provided the empirical formula Sr 1.86 Ca 1.13 Ba 0.02 K 1.47 Na 0.48 (Al 7.79 Fe 0.13 Si 8.08 O 32.025 )·14.97H 2 O. The mineral is orthorhombic, space group P 2 1 2 1 2, a = 14.1790(2), b = 10.6062(2), c = 13.8989(2) Å, V = 2090.19(6) Å 3 and Z = 2. The crystal structure of the mineral ( R = 0.0374 for 4963 unique reflections with I > 2σ( I )) is characterized by the gismondine-type (GIS) framework with ordered Al and Si atoms in tetrahedral sites. Partially ordered extra-framework cations and water molecules fill the cages of the framework. The higher hydration degree increases the ordering of extraframework cations in the structure. The higher hydration degree increases the ordering of extraframework cations in the structure. The phenomenon is discussed in ion-exchanged GIS zeolites as well as natural zeolites of PHI-type structures.

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)0.9F0.1 from the Shuk-Byul rare-metal granite pegmatites (Sangilen Highlands, Tuva) and amblygonite LiAlPO4F0.5(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 Δ_fH_el^0 (298.15 K) = –2326.3 ± 2.2 kJ/mol for montebrasite with the composition LiAl(PO4)(OH)0.9F0.1 and for amblygonite with the composition LiAl(PO4)F0.5(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 Δ_fG_el^0 (298.15 K) for intermediate and end members of the amblygonite–montebrasite series are estimated.

New data on the crystal structure, chemical composition, and nature of extra-framework components of the orthorhombic sodalite-group mineral vladimirivanovite were obtained using chemical and single-crystal X-ray diffraction data as well as infrared and Raman spectroscopy. The crystal structure of vladimirivanovite is based on the sodalite-type aluminosilicate framework with ordered Al and Si atoms. Sodalite-like cages are mainly occupied by Na+ and Ca2+ cations and (SO4)2− anions. It was shown that vladimirivanovite is characterized by significant variations in the content of extra-framework polysulfide groups (S3•−, S4), as well as other neutral molecules (H2O and CO2), the presence of which in the structure is the main cause of structural modulations and the orientation disordering of sulfate anions. Three samples with different S3•−:S4 ratios were studied. All of them are orthorhombic (space group Pnaa) with the unit-cell parameters a ≈ 9.1, b ≈ 12.9, and c ≈ 38.6 Å; Z = 6. The general crystal-chemical formula of vladimirivanovite is (Na+6.0–6.4Ca2+1.5–1.7)(Al6Si6O24)(SO42−,S3•−,S4)1.7–1.9(CO2)0–0.1·nH2O (n = 1–3), where the S4 molecule occurs in different conformation states.

New data on the crystal structure and isomorphism of extra-framework components in the cancrinite-group mineral tounkite have been obtained using chemical and single-crystal X-ray diffraction data, as well as infrared, Raman, ESR, UV–Vis–near-IR absorption and photoluminescence spectroscopy methods. The crystal structure of tounkite is based on the aluminosilicate framework formed by the САСАСВСВСАСВ stacking sequence with ordered Si and Al atoms The framework hosts Losod and liottite cages as well as columns of cancrinite cages. It is shown that tounkite is characterized by wide variations of the chemical composition. Its simplified crystal–chemical formula is (Na+3.89–5.18K+0.15–1.64Ca2+2.30–2.58(Al6Si6O24)(SO42−,S52−,S4) 2−x (Cl−, HS−)1+y·nH2O (x, y, n < 1). The S2⦁− and S3⦁− radical anions may occur in some tounkite samples in minor amounts. These crystal–chemical features indicate that tounkite crystallizes under highly reducing conditions. All studied tounkite samples were polysynthetic twins. A large 10-layed cage formed at the border between twin components, connected by a rotation of 180° around the [001] axis, which may host the large S52− anion.

Hydroxylbastn & auml;site-(La), the OH- and La-dominant member of the bastn & auml;site group, in fact known for many years, was studied in detail and has been approved by the IMA-CNMNC as a new mineral species with the ideal, end-member formula La(CO3)(OH). The holotype originates from the Vuoriyarvi (another spelling: Vuorij & auml;rvi) alkaline-ultrabasic complex, Northern Karelia, and the cotype from the Mochalin Log REE deposit, Potaniny Mts, South Urals, both in Russia. At Vuoriyarvi, hydroxylbastn & auml;site-(La) occurs as clusters (up to 1 mm) of light brown, honey-yellow or colourless hexagonal tabular to short-prismatic crystals up to 0.15 mm associated with fluorite and ancylite-(Ce) in cavities of calcite-dolomite carbonatites. At Mochalin Log, hydroxylbastn & auml;site-(La) forms light brown grains up to 0.2 mm included in massive aggregates of other LREE minerals: bastn & auml;site-(Ce), bastn & auml;site-(La), percleveite-(Ce), percleveite-(La), biraite-(Ce), biraite-(La), t & ouml;rnebohmite-(La), ferriperb & oslash;eite-(Ce), allanite-(Ce), etc. Dmeas is 4.75(2) and Dcalc is 4.778 g cm-3 (holotype). Hydroxylbastn & auml;site-(La) is optically uniaxial (+), omega = 1.76(1) and epsilon = 1.86(1) (holotype). The chemical composition (wt.%, electron microprobe, CO2 and H2O calculated: holotype/cotype) is: CaO 0.23/0.00, SrO 0.07/0.00, La2O3 39.47/39.58, Ce2O3 33.51/31.99, Pr2O3 1.03/1.51, Nd2O3 1.95/2.38, F 0.76/3.33, CO2 20.49/20.34, H2O 3.77/2.58, -O=F 0.32/1.40, total 100.96/100.31. The empirical formulae, calculated based on the sum of metal cations of 1 apfu and one CO3 group pfu, are (La0.52Ce0.44Nd0.02Pr0.01Ca0.01)Sigma 1.00(CO3)[(OH)0.90F0.09]Sigma 0.99 (holotype) and (La0.53Ce0.42Nd0.03Pr0.02)Sigma 1.00(CO3)[(OH)0.62F0.38]Sigma 1.00 (cotype). Hydroxylbastn & auml;site-(La) is hexagonal, P6, unit-cell parameters (from powder XRD data, holotype/cotype) are: a = 12.537(3)/12.533(1), c = 9.968(2)/9.908(1) & Aring;, V = 1356.8(5)/1347.9(3) & Aring;3 and Z = 18. Strong reflections of the powder XRD pattern [d,& Aring;(I)(hkl)] are (holotype): 4.98(39)(002), 3.616(88)(300), 2.926(100)(302), 2.089(41)(330), 2.052(46)(304) and 1.927(40)(332). The crystal structure of holotype hydroxylbastn & auml;site-(La) was refined by the Rietveld method, Rwp = 0.0071, Rp = 0.0050, Robs = 0.0466. It is isostructural to hydroxylbastn & auml;site-(Ce) and synthetic bastn & auml;site-type hydroxyl-carbonates REE3+(CO3)(OH) (REE = La-Er), but differs from fluorine-dominant bastn & auml;sites which adopt the space group P62c.

The crystal structure of zharchikhite, AlF(OH) 2 , from the Zharchikhinskoe deposit (Buryatia, Russia) is solved here using single-crystal X-ray diffraction. The mineral is monoclinic, space group P 2 1 /c , a = 5.1788 (4), b = 7.8386 (4), c = 5.1624 (4) Å, β = 116.276 (10)°, V = 187.91 (3) Å 3 and Z = 4. Zharchikhite demonstrates a novel structure type roughly related to the α-PbO 2 structure type and different from other compounds of the Al–F–OH system. The crystal structure of zharchikhite is based on the octahedral pseudoframework built from zigzag chains of edge-sharing AlF 2 (OH) 4 octahedra; adjacent chains are linked via F vertices and the pseudoframework contains wide channels.

The new mineral popugaevaite Ca3[B5O6(OH)6]FCl28H2O was found at the Internatsional'nyi diamond mine, Internatsional'naya kimberlite pipe, Sakha (Yakutia) Republic, Russia. It belongs to the low-temperature hydrothermal mineral assemblage formed in the contact zone between kimberlite and a boron-bearing halite rock. Popugaevaite occurs as veinlets in massive aggregates of ekaterinite and crusts (up to 0.7 mm thick and up to 1 cm x 4 cm in area) on ekaterinite nodules embedded in halite. Other associated minerals are Fe-rich szaib & eacute;lyite, serpentine, dolomite, pyrrhotite and chalcopyrite. Crude prismatic crystals of popugaevaite are up to 0.3 x 1 mm. The mineral is transparent, colourless, with vitreous lustre and perfect {010} cleavage. It is optically biaxial (-), alpha 1.502(2), beta 1.523(2), gamma 1.530(2) and 2Vmeas = 50(10)degrees. The chemical composition (wt.%, electron-microprobe, boron by ICP-MS, H2O calculated by stoichiometry) is: CaO 28.54, B2O3 28.62, F 3.19, Cl 11.50, H2O 32.83, O = (F,Cl) -3.94, total 100.74. The empirical formula, calculated based on 23 O+F+Cl and 22 H atoms per formula unit, is Ca3.07B4.96O6.03(OH)6F1.01Cl1.968H2O. Popugaevaite is monoclinic, space group Pn, a = 8.7055(11), b = 8.1025(11), c = 14.812(2) & Aring;, beta = 91.367(7)degrees, V = 1044.5(2) & Aring;3 and Z = 2. The strongest reflections of the powder X-ray diffraction pattern [d,& Aring;(I,%)(hkl)] are: 8.12(100)(010), 4.058(27)(020), 3.577(15)( $\bar 1$21), 2.936(10)(123), 2.834(16)(301, $\bar 1$05) and 2.283(10)(133). The crystal structure was solved based on single-crystal XRD data and refined on powder data by the Rietveld method, Rwp = 0.0058, Rp = 0.0043 and Robs = 0.0241. Popugaevaite is an isostructural analogue of brianroulstonite Ca3[B5O6(OH)6](OH)Cl28H2O with F- instead of the OH- group non-bound with boron. The structure is based upon the layers of twelve-membered rings of alternating BO3 triangles and BO2(OH)2 tetrahedra. The mineral is named in honour of the Russian geologist Larisa Anatol'evna Popugaeva (1923-1977), one of the principal discoverers of diamondiferous kimberlite pipes in Yakutia.

Spontaneous alpha-Si1-xGexO2 single crystals were synthesized using the set of crystal growth techniques: hydrothermal (X-Ge = 0.09, 0.20), flux (X-Ge = 0.45, 0.70) and recycling (X-Ge = 0.96). The XRD and spectroscopic studies with non-negative matrix factorization show linear dependences of structural parameters and Raman shift on germanium content and confirmed the existence of a complete series of alpha-Si1-xGexO2 solid solution. The synthesized samples of the solid solution were studied by Raman spectroscopy at the ambient conditions and for the first time at high pressures up to similar to 30 GPa. The obtained results suggest a phase transition "alpha-quartz -> post-quartz" for Si1-xGexO2 in the examined pressure range. The formation of the possible intermediate phase (quartz-II) was detected for Si1-xGexO2 with X-Ge = 0.09, 0.20 and 0.45 at 11, 10 and 7.5 GPa, respectively. The linear dependences of the pressure value of phase transitions on germanium content were observed. At decompression, the post-quartz phase remained stable that was determined by Raman spectra for all compositions of solid solution. Obtained experimental results revealed the correlation of the chemical composition, spectroscopic characteristics, and structural deformations at ambient conditions and at high pressures.

Atakamite with the empirical formula (Cu1.97Zn0.01)Cl0.94(OH)3.02, originating from the paleofumaroles of the monogenic volcano Vysota 1004 (Tolbachik, Kamchatka, Russia), has been studied by thermal and electron microprobe analyses, X-ray powder diffraction, IR and Raman spectroscopy, Calve microcalorimetry. Using X-ray diffraction and IR spectroscopy, the process of thermal decomposition of atacamite was studied. The enthalpy of formation from the 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. Based on the data obtained, thermodynamic modeling of the stability of atacamite in the Cu–O–Cl–H system was carried out, and the boundaries of its stability were calculated under conditions of high alkalinity and high acidity of the mineral-forming medium.

Destinezite ( Fe_1.97^3 + Al0.02)(PO4)0.99(SO4)0.90(OH)1.20⋅5.97H2O (Czech Republic) has been studied by thermal and electron-microprobe analyses, X-ray powder diffraction, and by IR, Raman, and Mössbauer spectroscopy. The enthalpy of formation of destinezite Fe_2^3 + (PO4)(SO4)(OH)⋅6H2O from elements ∆fH0(298.15 K) = –4258 ± 12 kJ/mol was determined by the method of solution calorimetry in lead borate 2PbO⋅B2O3 melt on a Setaram (France) Calvet microcalorimeter. The value of its absolute entropy S0(298.15 K) = 462.0 J/(mol K) was estimated, the entropy of formation ∆fS0(298.15 K) = –2054 J/(mol K), and the Gibbs energy of formation from the elements ∆fG0(298.15 K) = –3646 kJ/mol were calculated.

Strontioborite, which was first described in 1960 and later discredited by the then named Commission on New Minerals and Mineral Names of the International Mineralogical Association (IMA CNMMN), has been re-investigated (electron microprobe, single-crystal and powder X-ray diffraction, crystal structure determination and IR spectroscopy) on two specimens, including the holotype, and revalidated by the IMA Commission on New Minerals, Nomenclature and Classification (CNMNC). Strontioborite is known only at the Chelkar salt dome (North Caspian Region, Western Kazakhstan), in halite rocks with bischofite, magnesite, anhydrite, halurgite, boracite, ginorite and celestine. It forms colourless lamellar, scaly or tabular crystals up to 2 mm across. The chemical composition (wt.%, H2O is calculated for (OH)(4) = 4 H apfu, according to structural data; holotype/neotype) is: CaO 1.42/0.27, SrO 23.10/23.79, B2O3 67.37/67.57, H2O 8.73/8.72, total 100.62/100.37. The empirical formulae [calculated based on 15 O apfu = O-11(OH)(4) pfu] of the holotype and neotype specimens are Sr0.92Ca0.10B7.98O11(OH)(4) and Sr0.95Ca0.02B8.02O11(OH)(4), respectively. The idealised formula is Sr[B8O11(OH)(4)]. Strontioborite is monoclinic, space group P2(1), a = 7.6192(3), b = 8.1867(2), c = 9.9164(3) & Aring;, beta = 108.357(4)degrees, V = 587.07(3) & Aring;(3) and Z = 2. The strongest reflections of the powder X-ray diffraction pattern [d,& Aring;(I)(hkl)] are: 7.22(100)(100), 5.409(61)(110), 4.090(64)(020), 3.300(48)(210), 2.121(30)(24) and 2.043(37)(040, 024, 24). The crystal structure, solved from single-crystal X-ray diffraction data (R = 0.0372), is based upon the (100) layers of polymerised B-O-OH polyanions [B8O11(OH)(4)](2-) and Sr-centred nine-fold polyhedra SrO6(OH)(3). The B-O-OH polyanion is the cluster of three tetrahedra and three triangles; these clusters are decorated by the [B2O2(OH)3] pyro-group consisting of two triangles. The layers are linked via vertices of Sr-centred polyhedra, which share seven vertices with B-centred polyhedra of one layer and two vertices with B-centred polyhedra of the adjacent layer, and by the system of H bonds. The crystal chemistry of strontioborite is discussed in comparison with other natural and synthetic borates.