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.
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