This is a short article for the general public published in a Spanish speleological bulletin (Revista Calar). The article on moonmilk includes numerous photographs and diagrams and contains detailed but clear descriptions of the types of moonmilk, different mineralogies and their formation mechanisms.
F.27 Contribution to preserving/protecting natural and cultural heritage
In this conference contribution we discuss the biogenicity and origin of fibrous microcrystalline calcite (FMC) in calcareous soils, coarse-grained deposits and moonmilk speleothems. The origin of FMC, particularly needle fibre calcite, has received broad scientific interest and has been attributed either to purely physicochemical processes or to microbial (generally fungal) biomineralisation. In this workshop about microbes and their role in forming sediments, our hypothesis of a possible passive role of organic matter in FMC precipitation -an aspect mostly ignored in the previous studies- generated a constructive discussion in the audience.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 41299757In this biennial meeting of Slovenian geologists we presented a discussion on the possible biologically-induced versus biologically-influenced versus purely inorganic precipitation of fibrous microcrystalline calcite based on the project’s results. In order to strengthen the perception of non-classical crystallisation mechanisms in natural, geological settings, the presentation focused on showing the striking similarities between micro-morphological features of FMC observed under SEM and calcite crystals formed in vitro by non-classical pathways of crystallization, a concept that has only marginally entered disciplines like modern carbonate sedimentology, including its interdisciplinary research area dealing with biomineralisation.
B.06 Other
COBISS.SI-ID: 41468205This is a contribution (oral presentation) to the 25th International Karstological School where we presented the variety of moonmilk depositional facies and the structure of FMC precipitating microenvironments in these speleothems. Specifically, this work focuses on the observation of moonmilk on thin section under optical microscopy. Due to the high porosity and hydrated state of moonmilk, the preparation of thin sections is not simple, so most of the published studies of moonmilk have analysed the textures using only scanning electron microscopy. In this presentation we showed how it is possible to prepare good quality thin sections and how this technique provide a very valuable information, since we have been able to identify microfabrics, typical of microbial deposits such as peloids, crenular laminations, shrubs and septal alveolar textures. These results were very well received in the community of cave and karst scientists.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 41731117We presented our work in the Goldschmidt conference on Geochemistry, in a sesion named Spatial and temporal dynamics of early stages of mineral formation and micron-scale heterogeneities – insights from field, experiments and numerical approaches. This conference contribution presents some of the most interesting results of this project. Micro-morphological features of FMC observed under SEM are strikingly similar to those of calcite crystals formed in vitro by non-classical pathways of crystallization. The smooth character of the NFC rods, their spatial crystallographic orientation, and the presence of droplets or bobbles at the tip of the crystals are typical features of calcite fibres pre- cipitated by polymer-induced liquid precursor mechanisms (PILP). Single-crystal, high aspect ratio, flexible like nanofibres of similar sizes of those found in FMC in nature have been precipitated in the lab in the presence of Poly(Allylamine Hydrochloride) by aggregation of amorphous particles, which are incorporated into the fibres uniquely at their tips, before crystallizing. The systematic identification of these features in cave moonmilk and related settings in soils supports our hypothesis that microbial EPS can influence crystal morphology and growth of distinctive nonequilibrium forms of calcite without living organisms and metabolic processes directly involved in mineralisation.
B.03 Paper at an international scientific conference
COBISS.SI-ID: 41979437