Preliminary Data on the Nanoscale Chemical Characterization of the Inter-Crystalline Organic Matrix of a Calcium Carbonate Biomineral

Alberto Pérez-Huerta,Fernando Laiginhas

doi:10.3390/min8060223

Alberto Pérez-Huerta, Fernando Laiginhas

Open Access

https://doi.org/10.3390/min8060223

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Journal: Minerals	Publication Date: May 25, 2018
Citations: 10	License type: CC BY 4.0

Affiliation: Geological Survey of Alabama, University of Alabama

Abstract

Chemical signatures of carbonate biominerals are important for understanding biomineral formation, and are a subject of great interest in geosciences for applications in paleoclimatology and paleoceanography. A prominent unknown factor is the chemistry of organic matrices, in particular that of the inter-crystalline fraction. Here, we use atom probe tomography (APT) for the nanoscale chemical characterization of the mineral-organic interface in calcite from mussel shells. Our findings indicate that the quality of APT bulk chemistry results is highly dependent on sample preparation, yet data on biogenic calcite could be geochemically interpreted with confidence. Three-dimensional (3D) reconstructions of calcite tip specimens show the presence of organic matrix domains, characterized by the depletion of cations but enrichment in oxygen and carbon, and with at least 1% atomic increase in 16O relative to the surrounding mineral phase. This is the first relative, in-situ quantification of the chemical composition of the inter-crystalline organic matrix (IOM) for a carbonate biomineral, with implications for a better understanding of vital effects, proxy calibration, and the formation of these biocarbonates. Overall, our findings demonstrate the potential of nanoscale characterization of biominerals and their abiogenic counterparts to further advance our understanding of their chemistry.

Highlights

The study of calcium carbonate biominerals plays a very important role in the understanding of biomineralization processes (e.g., [1,2])
Our findings demonstrate the potential of nanoscale characterization of biominerals and their abiogenic counterparts to further advance our understanding of their chemistry
focused ion beam (FIB) work was more laborious on the near-perpendicular sections, requiring more time to fabricate the wedges and sharpen the tips, and faster on specimens extracted from sections containing the c-axis for prisms

Summary

Introduction

The study of calcium carbonate biominerals plays a very important role in the understanding of biomineralization processes (e.g., [1,2]). There are still fundamental aspects about the chemistry of these biominerals that are insufficiently known The absence of this chemical information has an impact in our knowledge of biomineral formation [3]. This can impact the correct interpretation of chemical proxy data from these biominerals, which is used for reconstructions of past climates, environments, and oceanic conditions [4]. One of those aspects relates to the chemical signature of organic matrices, as these biominerals are composites of mineral and organic phases [3]. The main component studied in the context of biomineralization is the inter-crystalline organic matrix (IOM)

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Conclusion