ISSN 1028-334X, Doklady Earth Sciences, 2011, Vol. 441, Part 2, pp. 1719–1723. © Pleiades Publishing, Ltd., 2011. Original Russian Text © N.S. Bortnikov, V.M. Novikov, T.S. Gendler, G.O. Piloyan, E.A. Zhegallo, N.M Boeva, 2011, published in Doklady Akademii Nauk, 2011, Vol. 441, No. 6, pp. 788–791. 1719 Biomineralization processes, i.e., the formation of minerals from living organisms, play an important role in nature [1]. The physical properties of minerals that were formed as a result of biomineralization processes can be essentially different from their analogues formed during inorganic crystallization reactions. The products of reactions between organic and inorganic compounds have been found in different geological environments. They are widespread in the hypergene- sis zones, where iron bacteria take an active part in for- mation of iron oxides and hydroxides [2]. Currently, there is considerable interest in this problem among geologists and among chemists and biologists due to the opportunity to obtain new materials during bio- chemical reactions. Consequently, study of the products of natural biomineralization processes is important both for understanding the conditions of their formation and for modeling possible ways of their use in different bio- technology industries [3]. In this connection, iron concretions are of particular interest, as their structure and composition reflect the role of biochemical reac- tions in their deposition [4–6]. In this work the results of detailed study of these formations are presented. During our works along with the ordinary methods such as X-ray analysis, electron microscopy, infrared spectrometry, and roentgen-flu- orescent analysis, magneto-thermal and thermal anal- ysis were used. We studied the iron concretion from an iron-bear- ing horizon (cuirasse) of the bauxite weathering crust of basalts of the deposit of Bao Lok in South Vietnam (Fig. 1a). The weathering crust forms under a wet tropical climate with alternate dry and wet seasons with an abundance of organic matter [7]. The main features of the concretion studied are the macro- and micro-heterogeneous structure due to the presence of crystalline and biomorphic aggregates and the magnetization of the concretion. Visually, six zones with different thickness, color, density, and mineral composition were distinguished in this concretion and material (samples 1–5) from every zone was sampled (Fig. 1b). The material from zones 1–5 was studied. Due to the small quantity, the material of the sixth zone was analyzed only by the X-ray method. During this study we established the presence of min- eralized bacteria in all the zones using CamScan-4 (Cambridge) and TESCAN VEGA IIXMU (Tescan) scanning electron microscopes. Bacteria are mainly represented by coccoid spe- cies, a size of which varies from 0.1 to 1.5 μm; only in the second zone were large individuals with a diameter of up to 10 μm noted. Small coccoid bacteria form dome-shaped and spherical colonies and other struc- tures up to 300 μm in size (Fig. 2). In some cases coccoides are united into longitudi- nal chains, parallel to one another. Anyway, they can be referred to fossilized magnetite-bearing magneto- somes [3]. Tubular species with a diameter of about 10 μm, similar to Leptotrix, replaced by ferrihydrite [2] occur rarely. Crystalline aggregates consist mainly of stellate growths of needlelike goethite crystals with a size of about 1.5 μm. Biomineralization and Magnetic and Thermal Properties of the Iron Concretion from the Laterite Bauxite Deposit of Bao Lok, South Vietnam Academician N. S. Bortnikov a , V. M. Novikov a , T. S. Gendler b , G. O. Piloyan a , E. A. Zhegallo c , and N. M Boeva a Received September 23, 2011 DOI: 10.1134/S1028334X11120221 a Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Staromonetny per. 35, Moscow, 119017 Russia b Schmidt Joint Institute of Physics of the Earth, Russian Academy of Sciences, B. Gruzinskaya ul. 10, Moscow, 123995 Russia c Borisyak Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya ul. 123, Moscow, 117997 Russia e-mail: boeva@igem.ru GEOCHEMISTRY