Answers are grounded in this paper and cite their sources.
Amorphous calcium carbonate phases, either synthesized artificially or generated biogenically, can be identified from broadened peaks in X-ray or electron diffraction profiles. It is conceivable that randomly oriented nanocrystals, approximately 1 nm in size, could give rise to coherent diffraction profiles that are characterized as amorphous. The coherent diffraction profiles for 200 keV electrons, as might be used in an electron microscope, and Cu Kα X-rays were calculated for needle-shaped calcite crystals bounded by \{ {11 21}\} facets and rhomb-shaped crystals bounded by \{ {10 14} \} facets. Crystals of about 1.0 nm in size gave a profile that is consistent with the X-ray measurements of amorphous calcium carbonate. The relative intensity of high-angle broadened peaks and changes in the IR spectrum are best explained by disorder in the nanocrystallites. The presence of randomly oriented nanocrystallites also explains the lack of optical birefringence.
No takes yet. Share an insight, caveat, or question.
Rez et al. (2014) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: