We present the results of an aggregation study on the intrinsically disordered biomineralisation peptide n16N, which selects the aragonite polymorph of calcium carbonate and is expected to have aggregation-dependent structure and function. The peptide is a sub-sequence of the in vivo protein n16, with putative framework and polymorph selection roles in the nacre layer of pearl oyster (Pinctada fucata). Employing the intermediate-resolution coarse-grained protein model PLUM*, which has previously been validated with respect to n16N, we simulate assemblies of these peptide units for system sizes inaccessible to atomistic models. We use extensive conformational sampling to show that the configurational ensemble explored by n16N aggregates contains a significant proportion of ordered (Formula presented.)-structure, within which arrangement of monomers is consistent with a previous hypothesis on functionally distinct subdomains of n16N. We also study an n16N mutant which fails to aggregate in experimental studies and obtain very similar behaviour, the consequences of which are discussed.