Anyways can anyone tell me definitively what this stuff is/was for please?

I've collected so many I could probably melt them down and build a shed out of it by now. It's very light so I'm assuming its aluminium shrapnel from incendiary bombs dumped into the sea and washed up on shore? Maybe with phosphorus? Unfortunately it gives a good signal on the euroace and covers most Devon beaches, and it shares the same discrim notch as some precious metals, tempting me to dig every time,