[Blueflag]

Don’t phosphorous and sodium burn when dry? Or is just sodium.

‘rocks’ dried - ignited.

??

[Idaho_Cowboy]

Elemental sodium and potassium react violently with water and explode. Phosphorus will burn even when wet, though I'm not sure what it takes to start it burning.

[Oztrich Boy]

Don’t phosphorous and sodium burn when dry? Or is just sodium.

Posphorus burns when dry. It should be kept wet for storage.

Sodium slowy oxidises when dry. In the presence of water, it burns intensely. It should not be kept wet for any kind of storage.

[Kenika]

Could this be remnants of off shore fireworks displays. Not much on chemistry but it sure smells like it.