Star Sand - a small vial
This is called 'star sand' because it looks like stars, obviously ;-D.
It's actually the shells of tiny organisms and can only be found on a few remote islands in the pacific, most notably in Japan. This sand is from Hatoma Island on Okinawa.

I didn't go there myself. But it is allowed to be harvested and sold in small amounts.

It's very delicate, so you may just want to keep it for your Cabinet of Curiosities!