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., 2013; Gilis et al., 2014; Sun et al., 2020) but can also be found in fish otoliths (Gauldie, 1993; Falini et al., 2005; Chakoumakos et al., 2019), crustacean statoliths (Wittmann, Schlacher & Ariani, 1993), eggshells (Vianey-Liaud et al., 1997; Nys et al., 1999, 2004), sponges (Jackson, Thiel & Wörheide, 2010), humans (i.e. in kidney stones; Sokol et al., 2005; Al-Atar et al., 2010; Evan et al., 2015) and in molluscs (Wu, Chiang & Zhou, 2017).