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Published on: April 24, 2016
Evaluating the single crystallinity of sea urchin calcite
Sebastian Hoerl1, Erika Griesshaber1, Antonio G Checa2
1Department für Geo- und Umweltwissenschaften, Ludwig-Maximilians-Universität München, Munich 80333, Germany.
Acta Biomaterialia
|March 28, 2025
Summary
Sea urchin calcite is not a single crystal. Advanced electron backscatter diffraction (EBSD) reveals internal misorientations in the microstructure of sea urchin tests and spines, challenging previous assumptions.
Area of Science:
- Biomineralization
- Materials Science
- Paleontology
Background:
- Sea urchin skeletons (tests and spines) are lightweight biomaterials composed of interlinked calcite crystals.
- The crystallographic organization and degree of crystallinity in echinoid calcite are not fully understood.
- Conventional electron backscatter diffraction (EBSD) has limitations in precisely measuring crystal misorientations.
Purpose of the Study:
- To investigate the microstructure and crystallographic texture of sea urchin (Cidaris cidaris and Paracentrotus lividus) test and spine calcite.
- To re-evaluate the widely accepted notion of single-crystallinity in sea urchin calcite using advanced EBSD techniques.
- To determine the precise misorientation between calcite crystals in echinoid skeletal elements.
Main Methods:
- Utilized advanced electron backscatter diffraction (EBSD) pattern matching data evaluation for high-precision misorientation detection (<0.1°).
- Analyzed the microstructure and crystallographic texture of calcite from Cidaris cidaris and Paracentrotus lividus tests and spines.
- Compared results with conventional EBSD data evaluation (0.5°-1° misorientation precision).
Main Results:
- Sea urchin tests and spines are not single crystals but comprise calcite with varying fabrics and co-orientation strengths.
- Significant internal misorientations (1-3°) were found in both test and spine portions.
- Spines exhibit a bimodal crystal texture with co-oriented calcite cores and misoriented crystal cortices, likely due to competitive growth.
Conclusions:
- The study demonstrates that echinoid calcite is polycrystalline, featuring internal misorientations and poorly co-oriented regions.
- Advanced EBSD reveals intricate microstructures previously undetected, revising the understanding of sea urchin skeletal material.
- Understanding echinoid calcite's crystallinity and organization is crucial for comprehending their exceptional structural and material properties.
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