any ideas?

I was cleaning my grandmother’s house and found this tin containing this double bagged dust with little pebbles in it.
Don’t think it’s someone’s ashes as it’s so rocky … anyone got any idea why this would be double bagged and put in a tin?
My grandma isn’t here to ask her any more💔
She was into rocks, especially tumbling them, but this doesn’t seem like something that would have normally fascinated her.