Vol CLIV, No 2 (2025)

Amazonite zonal pegmatites and associated dikes of pegmatoid granites have a special position among rare-metal and rare-earth pegmatites. The geological and structural situation of the localization (including the lack of connection with granite plutons) and the internal structure of their fields have certain similarities with the fields of rare-metal sodium-lithium spodumene pegmatites. With this similarity, the compositions of pegmatites are fundamentally different: the former are classified as representatives of the NYF (Nb-Y-F) family of pegmatites, the latter as typical pegmatites of the LCT (Li-Cs-Ta) family. Certain differences in mineralogical features are also established among amazonite pegmatites of different fields: for example, amazonite pegmatites of Western Keivy (Kola Peninsula) and amazonite pegmatites of Ilmeny (Ural), in which minerals characteristic of lithium pegmatites become common. On the other hand, there are known fields of spodumene pegmatites (Tastyg, Tuva), where spodumene is associated with amazonite and accessories common to аmazonite rare-metal-rare-earth pegmatites. There are some kind of transitions from amazonite pegmatites similar to the NYF family (Keivy) through amazonite pegmatites with mixed NYF+(LCT) features (Ilmeny) to amazonite-containing spodumene pegmatites with LCT+(NYF) characteristics (Tastyg, Tuva) and further to typical rare-metal non-amazonite pegmatites LCT. Based on the principles of the geological and petrological approach, a scheme for the systematization of granite pegmatites is proposed.

Morphological and kinetic characteristics of continuous transition through the saturation point from dissolution to growth on the same monomolecular steps on the crystal surface prove that growth and dissolution in the kinetic regime are irreversible processes at the nanoscale. Experimental modeling to solve the fundamental problem of the reversibility of growth and dissolution was carried out using atomic force microscopy (AFM) at extremely low crystallization rates of a poorly soluble model crystal in low-viscosity solutions. The result obtained extends the understanding of near-equilibrium crystal growth processes and the mechanisms of zonality formation in crystals.

The new natural Zn₂Al-Cl layered double hydroxide (LDH) has been discovered among pro-ducts of the supergene alteration of sphalerite-rich ores at the Hilarion mine, Lavrion District, Attikí Prefecture, Greece. It forms intergrowth with wermlandite-like LDH and unidentified mineral phases. The chemical composition is (wt %, electron microprobe, H₂O content is calculated by stoichiometry): ZnO 51.89, Al₂O₃ 16.09, As₂O₅ 1.83, Cl 10.08, H₂O 22.87, –O=Cl₂ –2.28, total 100.50. The empirical formula calculated on the basis of the sum of all metal atoms equal to 3 apfu is Zn_2.01Al_0.99(OH)_5.94Cl_0.90(AsO₄)_0.05×H₂O. Associated minerals are aluminoceladonite (phengite), quartz, calcite, smithsonite, adamite, insufficiently studied LDHs, and goethite. The new natural Zn₂Al-Cl LDH occurs as aggregates of split platy crystals up to 70 μm across and up to 10 μm thick. It has Mohs hardness about 2, mica-like cleavage on (001) and malleable tenacity. It is white with pearly lustre. The Zn₂Al-Cl LDH crystallizes in space group R-3m, the unit-cell parameters are: a = 3.073(4), c = 23.14(3) Å, V = 189.1(6) ų. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 7.71 (100) (003), 3.857 (52) (006), 2.594 (29) (012), 2.307 (40) (015), 1.9585 (11) (018). The calculated density is 2.78 g·cm^–3. The natural Zn₂Al-Cl LDH is optically uniaxial (+); w = 1.576(3), N_max = 1.592(3). Chemically, the studied new natural LDH is a Zn-analogue of chlormagaluminite that explains similarities in their infrared spectra. The closest structural analogue is 3R polytype of iowaite that is also a chloride LDH, while chlormagaluminite is known as 2H polytype only.

Based on the literature and original data, an attempt to characterize the isomorphism in the native tellurium — native selenium series has been made. A Se-enriched variety of native tellurium from the Ozernovskoe gold deposit (Kamchatka, Russia) is described. This very rare variety of native tellurium is widespread here. It forms nests and veinlets up to 10 cm thick and sometimes over 1 m long, clusters of needle-like to columnar crystals up to 1 cm long. Quartz, dickite, pyrite, maletoyvayamite, fahlores of the goldfieldite subgroup, fischesserite, gachingite, bohdanowiczite, and paraguanajuatite are associated with it. The Se content in the native tellurium from the Ozernovskoe deposit varies from 0.00 to 29.9 wt%; the latter value corresponds to the formula (Te_0.59Se_0.41). Using powder X-ray diffraction and scanning electron microscopy, the homogeneity of native tellurium samples from Ozernovskoe containing 12.5, 17.8 and 29.5 wt % Se, as well as its belonging to the isomorphous tellurium-selenium series were confirmed. Probably, a complete isomorphous series in the Se‒Te system is realized in nature, however, based on recent literature data, it can be assumed that ordered compounds of this system can also be formed in nature. A new type of gold-bearing mineralization, with maletoyvayamite and gachingite as the main mineral forms of gold, has been discovered in the ores enriched with native tellurium at the Ozernovskoe deposit.

Tourmalines of quartz-tourmaline altered rock (tourmalinite) belonging to argillic assemblage at the Terlig-Khaya mercury deposit in Tuva have been studied using scanning electron microscopy, electron microprobe analysis, laser ablation — inductively coupled plasma mass spectrometry, infrared spectroscopy, and Mössbauer spectroscopy. The tourmalines studied are primarily classified as foitite and oxy-foitite; some compositions are attributed to dravite, oxy-dravite, magnesio-foitite, and oxy-schorl. They are enriched in Ca (adachiite component) and Cl. The characteristic substitutions in tourmalines are Mg ↔ Fe²⁺, Na + Mg ↔ X-site vacancy + Al and Na + Si ↔ Ca + Al. The content of most measured trace elements in tourmalines does not exceed a few ten ppm. The Fe³⁺/Fe_tot (18 %) determined in bulk tourmaline sample indicate weak oxidizing conditions of the tourmalinite formation. Possible source for Cl and B in hydrothermal fluids is evaporites of the Tuva through.

Number of members and the activities of the Russian Mineralogical Society in 2024 are reported.