Scoria

In earlier terminology, scoria was usually defined with a size range, e.g. 2 to 24 mm (0.079 to 0.945 in) in diameter, but neither color nor composition was typically a part of the definition.

[5][6] During the 1980s, the size range disappeared from the definition, and a requirement was added that scoria be black or reddish in color and/or mafic in composition.

The difference is probably the result of lower magma viscosity, allowing rapid volatile diffusion, bubble growth, coalescence, and bursting.

Because of its good insulating properties, such roadbeds protect the ground beneath them from frost heave and heat deformation.

[7] It is also spread as a traction aid on ice- and snow-covered roads, and around oil wells to firm up mud produced by heavy truck traffic.

Because it can hold water in its vesicles and in the pore space between grains in aggregates, it can improve the water-holding capacity of planting soils.