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<p>We describe a quantitative statistical and geometric analysis of classical and non-classical modes of twinning in the calcite produced by biomineralization in the shell of the rotaliid foraminifer species <i>Amphistegina lessonii.</i> Foraminifera are responsible for about a quarter of the marine production of CaCO<sub>3</sub> and thus play a major role in the natural CO<sub>2</sub> sequestration into marine carbonate sediments. The shell calcite of rotaliid foraminifera is nano-twinned and thus quite distinct from inorganic calcite and from biogenic calcite produced by other groups of organisms. Previous work showed that foraminiferal calcite contains a high spatial density of twin walls of the classical 60°|&lt;001&gt; = m.{001} twin, but there was another peak in the range between 75° and 80° in the misorientation statistics of electron backscatter diffraction (EBSD) maps of the same specimen. We checked the significance of all maxima in misorientation by in-depth statistical analysis, thus confirmed the 60°|&lt;001&gt; penetration twinning and found that the 75°–80° maxima are related to new, non-classical, but systematically reoccurring oriented associations of calcite crystals with orientation relationships 78.2°|&lt;991&gt; and 76.6°|&lt;6&#xa0;−6 1&gt;. If the nano-twinning provides an evolutionary advantage, it may increase the strength and toughness of the feeble mineralized chamber walls of the organisms.</p>

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Statistical analysis of EBSD data confirms pronounced classical and non-classical pervasive crystallographic twinning in rotaliid foraminiferal calcite

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  • 发表日期：

    2025年4月28日

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  • Wolfgang W. Schmahl,
  • X. Yin,
  • J. Lastam,
  • E. Griesshaber,
  • S. Hoerl,
  • E. Sturm,
  • A. Sancho Vaquer

摘要

We describe a quantitative statistical and geometric analysis of classical and non-classical modes of twinning in the calcite produced by biomineralization in the shell of the rotaliid foraminifer species Amphistegina lessonii. Foraminifera are responsible for about a quarter of the marine production of CaCO3 and thus play a major role in the natural CO2 sequestration into marine carbonate sediments. The shell calcite of rotaliid foraminifera is nano-twinned and thus quite distinct from inorganic calcite and from biogenic calcite produced by other groups of organisms. Previous work showed that foraminiferal calcite contains a high spatial density of twin walls of the classical 60°|<001> = m.{001} twin, but there was another peak in the range between 75° and 80° in the misorientation statistics of electron backscatter diffraction (EBSD) maps of the same specimen. We checked the significance of all maxima in misorientation by in-depth statistical analysis, thus confirmed the 60°|<001> penetration twinning and found that the 75°–80° maxima are related to new, non-classical, but systematically reoccurring oriented associations of calcite crystals with orientation relationships 78.2°|<991> and 76.6°|<6 −6 1>. If the nano-twinning provides an evolutionary advantage, it may increase the strength and toughness of the feeble mineralized chamber walls of the organisms.