Research into invertebrate carbonate mineralogy has often discovered both variety and range in their skeletal calcite. Echinoderms are one such class of complex organisms which produce very specific calcite which aid in activities including feeding, predation protection, mobility, and structural support. Sand dollars are a global order of irregular echinoids (Clypeasteroida) in this class with distinctively flattened discoidal bodies covered in small spines. Their notable "squashed" shells, called tests, have garnered scientific study in fields of materials science, architecture and chemistry. Scientists have investigated the internal support structure, calcite formation and building process of tests and spines. Following investigations of biomineralization at the atomic level, we utilized scanning electron microscopy (SEM) to focus our investigation. Skeletal composition the New Zealand sand dollar, Fellaster zelandiae, was analysed via x-ray diffraction (XRD) to understand skeletal differences within individuals, within population clusters and among populations. Our data investigated the genotype versus phenotype differences in skeletal carbonate of sand dollars to better understand how these animals respond to environmental conditions as they produce biomineral calcite. Additionally, mineralogy of endemic Fellaster zelandiae was placed in the broader context of global sand dollar composition to investigate how the New Zealand species may differ from global populations.