Before revision: Grain size Volcanic ash grain size distributions from four volcanic eruptions Volcanic ash consists of particles (pyroclasts) with diameters < 2 mm (particles > 2 mm are classified as lapilli), and can be as fine as 1 μm.
After revision: Grain size Volcanic ash grain size distributions from four volcanic eruptions Volcanic ash consists of particles (pyroclasts) with diameters less than 2 mm (particles larger than 2 mm are classified as lapilli), and can be as fine as 1 μm.