Nature has long encoded structural intelligence into the mineral matrices of bones and shells, arranging organic molecules with a precision that materials science has struggled to replicate. A team of researchers has now uncovered a governing principle behind this order: the surface chemistry of nanoparticles, not their size or shape, determines where they come to rest within a growing crystal. By demonstrating that polymer nanoparticles spontaneously sort themselves into distinct zones of calcite based on their chemical coatings, the researchers have translated a lesson from biomineralization