Morpho-Mineralogical and Bio-Geochemical Description of Cave Manganese Stromatolite-Like Patinas (Grotta del Cervo, Central Italy) and Hints on Their Paleohydrological-Driven Genesis

Caves are dark subsurface environments with relatively constant temperatures that allow studying bio-mineralization processes and paleoenvironmental or climate changes in optimal conditions. In the extreme and oligotrophic cave environment, manganese patinas having stromatolite-like features are uncommon. Here we provide the first detailed mineralogical, geochemical, and microbiological investigation of fine-grained and poorly crystalline MnFe stromatolite-like wall patinas formed in a deep-cave environment in Italy. These mineralizations, about 3 mm thick, consist of an alternation of Mn-layers and Fe-lenses. We show that the microbial communities' composition is dominated by Mn-oxidizing bacteria, such as Bacillus, Flavobacterium, and Pseudomonas. Our multidisciplinary investigation, integrating data from different analytical techniques (i.e., optical microscopy, SEM-EDS, μXRF, XRPD, FT-IR, Raman spectroscopy, and DNA sequencing), revealed peculiar chemical, mineralogical, and biological features: 1) A cyclical oscillation of Mn and Fe along the growth of the patinas. We propose that this oscillation represents the shift between oxic and suboxic conditions related to different phases occurring during paleo-flood events; 2) A typical spatial distribution of mineralogy and oxidation state of Mn, bacterial imprints, detrital content, and stromatolite-like morphologies along the Mn-layers. We propose that this distribution is controlled by the local hydraulic regime of the paleo-floods, which, in turn, is directly related to the morphology of the wall surface. Under less turbulent conditions, the combination of clay mineral catalysis and biological oxidation produced vernadite, a poor-crystalline phyllomanganate with a low average oxidation state of Mn, and branched columnar stromatolite-like morphologies. On the other hand, under more turbulent conditions, the sedimentation of clay minerals and microbial communities' development are both inhibited. In this local environment, a lower oxidation rate of Mn2+ favored the formation of todorokite and/or ranciéite, two compounds with a high average oxidation state of Mn, and flat-laminated or columnar stromatolite-like morphologies

Presence and zoning of hydrous components in leucite from the Albani Hills volcano (Rome, Italy)

This paper reports a single-crystal FTIR spectroscopic study of leucite, a nominally anhydrous mineral (NAM). Several transparent, inclusion-free samples from different occurrences and localities in the Alban Hills volcanic area (Latium, Italy) were analyzed. The FTIR spectra collected in the 4000-3000 cm(-1) H2O-stretching region show a broad absorption consisting of overlapping components at 3604, 3500, and 3245 cm(-1). The occurrence of a well-defined combination band at 5225 cm(-1) indicates that almost all the examined samples contain hydrous components in the forth of structurally bound water molecules. Using the integrated molar absorption coefficient from the working curve of Libowitzky and Rossman (1997), a water content up to >4000 ppm was obtained for the studied specimens. Detailed microspectroscopy mapping shows significant zoning of water in some samples, typically consisting of an anhydrous core mantled by a hydrous rim. The collected data suggest that careful study of the distribution of the volatile content of leucite (and associated volcanic NAMs) may provide a tool to monitor the evolution of the magmatic system where these minerals occur

Channel CO2 in feldspathoids: a review of existing data and new perspectives

The study of volatile constituents in minerals has potential applications ranging from environmental studies to ore research to volcanic hazards. In this paperwe present new data on the volatile (particularly CO(2)) content of a series of feldspathoids belonging to the cancrinite-sodalite group of minerals, in combination with other data collected over the last few years. The work has been essentially done using FTIR microspectroscopy to detect and characterize the speciation of H and C in the micropores of these minerals. We show that most cancrinite-sodalite group of minerals are able to trap CO(2) in their structure in addition to other molecular and anionic species such as H(2)O, OH, F, Cl, SO(4), SO(3) etc. A combination of in situ and annealing heat-treatments shows that the different species in the cancrinite-sodalite group release CO(2) at different temperatures, due to the different connectivity of their pores. Detailed FTIR microspectrometry mappings typically show non-homogeneous distributions of hydrogen and carbon across the samples, and suggest a possible use of these minerals as a tool for geothermometric modelling. The finding that most cancrinite-sodalite group minerals are able to trap carbon dioxide opens a new frontier in the design of materials having potential for carbon sequestration from the atmosphere

Channel CO₂ in feldspathoids: new data and new perspectives

The study of volatile constituents in minerals has potential applications ranging from environmental studies to ore research to volcanic hazards. In this paperwe present newdata on the volatile (particularlyCO2) content of a series of feldspathoids belonging to the cancrinite-sodalite group of minerals, in combination with other data collected over the last few years. The work has been essentially done using FTIR microspectroscopy to detect and characterize the speciation of H and C in the micropores of these minerals. We show that most cancrinite-sodalite group of minerals are able to trap CO2 in their structure in addition to other molecular and anionic species such as H2O, OH, F, Cl, SO4, SO3 etc. A combination of in situ and annealing heat-treatments shows that the different species in the cancrinite-sodalite group release CO2 at different temperatures, due to the different connectivity of their pores.Detailed FTIR microspectrometry mappings typically show non-homogeneous distributions of hydrogen and carbon across the samples, and suggest a possible use of these minerals as a tool for geothermometric modelling. The finding that most cancrinite-sodalite group minerals are able to trap carbon dioxide opens a new frontier in the design of materials having potential for carbon sequestration from the atmosphere

Volatiles in cancrinite-sodalite group minerals

The minerals of the cancrinite-sodalite group are characterized by layers of six-membered rings of tetrahedra: each ring is linked to three rings in a preceding layer and to three rings in the succeeding one, such as to form a three dimensional framework (Bonaccorsi and Merlino 2005). Different stacking sequences give rise to different structures leading to cages, channels and cavities filled by extra-framework anions and cations. Common anions within the structural channels are Cl-, F-, SO42- and CO32-. Recent studies have however shown that carbon dioxide is also a common constituents of these minerals (Della Ventura et al. 2005, 2007a, 2007b). Other possible molecules are H3O+ or HCO3- groups (Gesing and Buhl 2000, Galitskii et al. 1978). IR spectroscopy allows the detection and possibly quantitative analysis of structural H-C-O species, and is thus particular suitable for characterising these minerals. We relate here the recent developments of our micro-FTIR and crystal-structure studies on a series of cancrinite-sodalite group minerals. Spectra were collected on well-characterized samples, mostly on oriented, doubly-polished slabs, with polarized radiation, using a NicPlan microscope equipped with a nitrogen-cooled MCT detector, a KBr beamsplitter and a ZnSe wire-grid IR polarizer. Microspectrometric mappings were acquired with a Hyperion 3000 Bruker microscope equipped with a computer-controlled motorized stage. HT spectra were collected using a Linkam FTIR600 heating stage (single-crystals) or a Specac HT/HP cell (powders). Single-crystal FTIR spectra show the common presence of CO2 in most samples, from a wide variety of geological provenance. In particular, systematically high amounts of CO2 are detected in franzinite, nosean and hauyine, while minor but significant amounts are found in vishnevite, marinellite, giuseppettite, vishnevite, davyne and sodalite. Polarized-light spectra collected on [001] sections of hexagonal cancrinite-group minerals show in all cases maximum absorption with E c, suggesting that the linear CO2 molecules are oriented perpendicular the crystallographic c axis of the mineral, like in beryl or cordierite (Aines and Rossman 1984). Combination of in situ and annealing high-T experiments shows that in the different species the carbon dioxide molecules are bound in different ways within the structure. In addition, release of CO2 occurs at significantly different temperatures due to the different connectivity of the structural pores. Detailed microspectrometry mappings shows non-homogeneous distributions of hydrogen and carbon across the samples, and suggest a possible use of these minerals as a tool for geothermometric modelling. The finding that most cancrinite-sodalite group minerals are able to trap carbon dioxide opens a new frontier in the design of materials having potential for carbon sequestration from the atmosphere. References Aines, R.D., Rossman, G.R. (1984) Am. Mineral., 69 319-327. Bonaccorsi E., Merlino S. (2005) In G. Ferraris and S. Merlino, eds., Micro- and Mesoporous Mineral Phases, p. 241-290. Reviews in Mineralogy and Geochemistry. Della Ventura G., Bellatreccia F., Bonaccorsi E. (2005) Eur. J. Mineral., 17, 847-851. Della Ventura G., Bellatreccia F., Parodi G.C., Cámara F., Piccinini M. (2007a) Am. Mineral. (in press). Della Ventura G., Bellatreccia F., Piccinini M. (2007b) Rend. Fis. Acc. Lincei (submitted). Galitskii, V.Yu., Grechushnikov, B.N., Sokolov, Yu.A. (1978) Russian J. Inorg. Chem., 23, 1749-1750. Gesing, M., Buhl, J.-Ch. (2000) Z. Kristallog., 215, 413-418

Water in leucite, a nominally ahydrous volcanic mineral

The study of magmatic/volcanic volatiles is based on the determination of H2O and CO2 in glasses, presuming they represent the vast majority of the gas dissolved in the melt. However, recent work shows that several nominally anhydrous volcanic minerals (NAMs) do contain trace but significant water ( CO2). Leucite - KAlSi2O6 - is an anhydrous mineral typical of potassium-rich basic lavas. It is commonly altered into analcime due to percolating Na-rich fluids during cooling of the host rock. The process is not a solid-state reaction but proceeds by dissolution of leucite and reprecipitation of analcime (Putnis et al. 2007). We report here a single-crystal FTIR study of transparent, inclusion-free leucite phenocrystals occurring within lava flows, pyroclastic deposits and ejecta in the Roman Comagmatic Province. The IR spectra invariably show broad absorptions in the 4000-3000 cm-1 region consisting of overlapping components around 3604, 3500 and 3250 cm-1, thus showing that the examined samples contain structurally bound water molecules. Detailed FTIR mappings, obtained using an automated stage, show significant zoning of this water, consisting typically of an anhydrous leucite core mantled by an hydrous rim. Micro-chemical data show almost negligible Na in the samples (< 0.5 wt% ), thus excluding alteration into analcime. Using the molar absorption value for analcime (Libowitzky and Rossman, 1996) H2O contents up to 700 ppm are calculated. This water is believed to be primarily incorporated in leucite together with trace Na in the structural pores. Its patterns of zoning may allow to monitor the evolution of magmatic system (P, T, fO2) as a function of time. Libowitzky, E and Rossman, GR (1996) Am. Mineral., 82, 1111-1115. Putnis, CV, Geisler, T., Schmid-Beurmann, P, Stephan, T and Giampaolo, C. (2007) Am. Mineral., 92, 19-26