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Microscopic fungi (micromycetes) play an important role in rock alteration often leading to formation of insoluble biogenic oxalates on rock/mineral surfaces. Oxalate crystallization under the influence of fungus Aspergillus niger (one of the most active stone destructors) was studied in vitro on two Mn,Ca-bearing minerals of manganese ores: todorokite (Na0.36,Ca0.09,K0.06,Sr0.03,Ba0.02)0.56(Mn5.53,Mg0.47)O12•3-4H2O and kutnohorite (Ca0.77,Mn0.23)(Mn0.74,Fe0.14,Mg0.11)(CO3)2. The underlying minerals and the products of their alteration were investigated using powder and single crystal X-ray diffraction, optical microscopy, SEM and EDX methods. It was shown that a more intense leaching of Ca-ions (compared to Mn-ions) from todorokite and kutnohorite leads to an earlier crystallization of calcium oxalates (predominantly whewellite) compared to manganese oxalates (lindbergite, falottaite). Crystallization of manganese oxalates on the surface of kutnohorite occurs in more acidic (compared to todorokite) medium through the formation of mycogenic Mn,Ca-bearing oxides, which are close in composition and structure to This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

To study strontium (Sr) incorporation into calcium oxalates (weddellite and whewellite), calcium-strontium oxalate solid solutions (Ca,Sr)[C2O4]∙nH2O (n = 1, 2) are synthesized and studied by a complex of methods: powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy. Two series of solid solutions, isomorphous (Ca,Sr)[C2O4]·(2.5 − x)H2O) (space group I4/m) and isodimorphous Ca[C2O4]·H2O(sp.gr. P21/c)–Sr[C2O4]·H2O(sp.gr. P 1 - ), are experimentally detected. The morphogenetic regularities of their crystallization are revealed. The factors controlling this process are discussed.

Rock surfaces in natural systems are inhabited by multispecies communities of microorganisms. The biochemical activity of microorganisms and the patterns of microbial crystallization in these communities are mostly unexplored. Patterns of calcium carbonate and calcium oxalate crystallization induced by bacteria Bacillus subtilis and by B. subtilis together with Aspergillus niger on marble surface in vitro in liquid medium and in humidity chamber—were studied. Phase identification was supported by XRD, SEM, EDXS; metabolite composition was determined by GC–MS. It was found that the activity of B. subtilis–A. niger associations significantly differ from the activity of B. subtilis monocultures in the same trophic conditions. The phase composition and the morphology of the forming crystals are determined by the composition of the metabolites excreted by the microorganisms—particularly by the ratio of the concentrations of extracellular polymeric substances (EPS) and oxalic acid in the medium. The acidification activity of micromycetes may suppress the formation of bacterial EPS and prevent the formation of calcite. The present results can be used in the development of biotechnologies using microbial communities.

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The method of chemodestructive fractionation is suggested to assess the composition of soil organic matter. This method is based on determination of the resilience of soil organic matter components and/or different parts of organic compounds to the impact of oxidizing agents. For this purpose, a series of solutions with similar concentration of the oxidant (K 2 Cr 2 O 7 ), but with linearly increasing oxidative capacity was prepared. Chemodestructive fractionation showed that the portion of easily oxidizable (labile) organic matter in humus horizons of different soil types depends on the conditions of soil formation. It was maximal in hydromorphic soils of the taiga zone and minimal in automorphic soils of the dry steppe zone. The portion of easily oxidizable organic matter in arable soils increased with an increase in the rate of organic fertilizers application. The long-lasting agricultural use of soils and burying of the humus horizons within the upper one-meter layer resulted in the decreasing content of easily oxidizable organic matter. It was found that the portion of easily oxidizable organic matter decreases by the mid-summer or fall in comparison with the spring or early summer period.