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Polycrystalline echinoderm calcite and its fracture mechanics
Science (New York, N.Y.)
|August 7, 1981
Summary
Sea star ossicles are made of polycrystalline calcite. Scanning electron microscopy revealed whisker-like calcite crystals arranged in spirals, potentially explaining echinoderm calcite
Area of Science:
- Marine Biology
- Biomineralization
- Materials Science
Background:
- Sea stars (Echinodermata, Asteroidea) possess skeletal ossicles.
- The microstructure of these ossicles is crucial for their mechanical properties.
Purpose of the Study:
- To investigate the microstructural organization of calcite in sea star ossicles.
- To correlate crystal morphology and arrangement with mechanical properties.
Main Methods:
- Scanning electron microscopy (SEM) was used to examine fractured skeletal ossicles of Echinaster spinulosus.
- Specimens were subjected to stress relaxation before fracturing to observe crystal behavior.
Main Results:
- Polycrystalline calcite was identified in the ossicles.
- Whisker-like calcite crystallites (1300 Å wide, ≥3600 Å long) were observed, packed in lamellae.
- Lamellae were arranged in spirals forming trabecular bars, with uniform crystallite alignment within an ossicle.
Conclusions:
- The observed crystallite packing and alignment in sea star ossicles may be influenced by geometric packing requirements.
- These geometric factors could explain the high magnesium ion concentration characteristic of echinoderm calcite.
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