Metamorphic veins record the fracture-controlled flow of fluids throug
hout the oceanic and continental crust. I show that the spatial distri
butions of veins from three diverse metamorphic settings are fractal a
nd self-similar. Vein densities were measured by counting the number o
f macroscopic veins intersected along linear transects. The localities
included wollastonite-quartz veins in marbles, for which the fractal
dimension D is 0.46, actinolite-chlorite veins in hydrothermally alter
ed oceanic diabases (D = 0.81), and epidote-quartz veins in contact-me
tamorphosed basalts (D = 0.25-0.63). The fractal clustering of veins p
rovides a geometric framework for understanding spatial and temporal p
atterns of fluid flow and mineral reaction during metamorphism.