The unique nano- and microstructure of twinned foraminiferal shell calcite

Lastam, J.; Griesshaber, Erika; Yin, Xiaofei; Rupp, Ulrich; Sánchez-Almazo, Isabel; Heß, M.; Walter, Patrick; Checa, António; Schmahl, Wolfgang W.

doi:10.21203/rs.3.rs-1688928/v1

Cited by 1 publication

(1 citation statement)

References 29 publications

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“…1: adjacent crystals always have similar colors. Misorientation was observed before in various biominerals 5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32 . The nanoscale misorientation of pairs of adjacent crystals, however, were never measured directly and quantitatively, and were never compared across diverse biominerals using the same method.…”

Section: Slight Misorientations Of Adjacent Crystals In Diverse Biomi...mentioning

confidence: 81%

Convergent, slightly misoriented crystals toughen corals and seashells

Gilbert

Lew

Stifler

et al. 2022

Preprint

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The hardest and toughest tissues formed by living organisms are organic-mineral composites termed biominerals 1,2. When they are crystalline, their mesostructure includes the nano- and micro-scale crystallite size, shape, arrangement, and orientation. Mesostructures vary enormously across marine CaCO3 biominerals (aragonite, vaterite, calcite) because they result from divergent evolution: biominerals were formed long after organisms diverged from one another 3,4. Despite such diversity, CaCO3 marine biominerals share a convergent character: adjacent crystals are similarly oriented 5-32. The reason for such convergence is unclear. Here, we show with quantitative, precise measurements at the nanoscale that the slight misorientation is consistently between 1°-40° in diverse biominerals. Can this slight misorientation confer a desirable materials property and therefore an evolutionary advantage to the forming organisms? We test and confirm this hypothesis with nanoindentation in diverse biominerals, geologic aragonite, and in abiotic, slightly misoriented, synthetic spherulites. Molecular dynamics (MD) simulations of bicrystals reveal that aragonite, vaterite, calcite, exhibit toughness peaks when they are misoriented by 10°, 20°, 30°, respectively, demonstrating that slight misorientation alone increases crack deflection and therefore fracture toughness. Slight misorientation, along with other previously known and co-existing toughening mechanisms, was selected repeatedly and convergently, during the course of evolution, to postpone fracture and thus provide organisms with competitive advantage. We anticipate slight misorientation-toughening to be a starting point for more sophisticated materials synthesis and additive manufacturing in many fields. Compared to previously known toughening mechanisms, in fact, the advantages of slight misorientation are that it can and does occur in synthetic materials, it requires one material only and no specific top-down architecture, it is easily achieved by self-assembly of organic molecules (e.g. aspirin, chocolate), polymers, metals, and ceramics 29 well beyond biominerals.

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