The precipitation of struvite (magnesium ammonium phosphate hexahydrate, MgNH 4 PO 4 ⋅6H 2 O) from wastewater is one of the most promising phosphorous recovery methods. This approach is already implemented to a limited extent , with no fewer than 40 industrial-scale treatment plants in operation worldwide, capable of mineralising up to 25% of the dissolved P from their agricultural waste stream . The recovered material is used as a phosphate replacement for natural ore deposits, i.e. phosphorites, or is consumed directly as a slow-release fertiliser. In addition, struvite formation can be locally problematic as it forms dense, persistent scale in pipes or filters, fouling and clogging components in water treatment plants. Therefore, struvite precipitation needs to be optimised to increase efficiency or to reduce the unintended occurrence of rapidly forming scale in engineered environments. One of the major challenges in achieving this goal is to understand the formation pathways of struvite from the early stages. For instance, the ability to detail specific stages of the crystallisation or the occurrence of transient (amorphous) precursors would allow for the development of targeted growth additives (e.g. water-soluble polymers) that give control over crystal shape, size or that stabilise intermediate (amorphous) stages .