Transitional spherulitic layer in the muricid Nucella lapillus

A sphere might be the most common crystal habit in nature as it exists in a wide range of organic and inorganic material systems (Shtukenberg et al., 2012). These crystal spheres are polycrystalline structures that feature a common centre of growth (CoG) from which acicular crystals radiate more or less uniformly outwards until the crystal aggregate forms a sphere. They are therefore called spherulites. Two types of spherulites are known: ‘spherical’, which grow as spheres, and ‘plumose’, which grow into elongated shapes. In a biomineralization context, spherulites occur most prominently in coral skeletons (Cuif & Dauphin, 2005; Nothdurft & Webb, 2007; van de Locht et al....