  Hydrated granular packings often crack into discrete clusters of grains when
dried. Despite its ubiquity, accurate prediction of cracking remains elusive.
Here, we elucidate the previously overlooked role of individual grain
shrinkage---a feature common to many materials---in determining crack
patterning using both experiments and simulations. By extending the classical
Griffith crack theory, we obtain a scaling law that quantifies how cluster size
depends on the interplay between grain shrinkage, stiffness, and
size---applicable to a diverse array of shrinkable, granular packings.
