Matalon-Packter law for stretched helicoids formed in precipitation processes

- We study helicoidal precipitation structures emerging in the wake of reaction-diffusion fronts.
- The precipitation helicoids are stretched, local pitch behind the front increases exponentially.
- The Matalon-Packter law is valid for precipitation helicoids as well.
- Results of the numerical simulations show similar behavior observed in experiments.
- The helicoids are self-assembled from building blocks of micron-size achiral spherulites.