Abstract
Under conditions of unobstructed diagenetic growth, opal-CT usually forms spherical aggregates, so-called “lepispheres”. From a scanning electron microscope study of deep-sea porcelanites, the development of these structures is described, from isolated opal-CT platelets via complete lepispheres to large coalescent aggregates. The conspicuous symmetric ultrastructure of lepispheres—reflected by the constancy of angles between interpenetrating crystal blades—is crystallographically determined: The lepispheres consist of groups of opal-CT blades intergrown according to the (30–34) and (10–16) twinning laws of tridymite. The same rules of intergrowth can be applied to the morphology of hydrothermally synthesized opal-CT lepispheres.
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Flörke, O.W., Hollmann, R., von Rad, U. et al. Intergrowth and twinning in opal-CT lepispheres. Contrib. Mineral. Petrol. 58, 235–242 (1976). https://doi.org/10.1007/BF00402354
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DOI: https://doi.org/10.1007/BF00402354