Definition of blue metal in English:

blue metal

noun

British
  • [mass noun] Broken blue stone used for road-making.

    • ‘With nature neatly surveyed, fenced and buried under bricks and blue metal, the need to assert their ascendancy over the natural world was reduced.’
    • ‘Instead of using lucerne hay, compost or cane tops to cover the beds, mulch should consist of hard materials such as gravel, pebbles or blue metal.’
    • ‘When we played kick-to-kick at school we did it on the gravel, when we played vigorous games at home we did it in a gravel backyard strewn with blue metal to keep the weeds at bay.’