[techhelpbb]

Fine silicon sand works but not instantly and you need enough sand to bury the fire and cut off the oxygen.

The sand will also take heat from the magnesium helping to bring the mass below ignition.

Be very careful: you need to keep adding sand for some time while eliminating other things that can ignite and this means you need to be close to a hot fire. The sand itself can be fuel in small quantites mixed into the magnesium dust. You need to bury and not mix.

There are several YouTube videos that show mixtures of magnesium dust and sand flaring up: in these cases the sand to magnesium ratio is too low and the 2 are mixed.