Undrilled round glass beads. The opaque colors look like tiny pearls. Add to a tiny bottle, like the Iridescent Glass Spheres linked below, or float in ICE Resin, or use glue or double-stick tape to adhere to collages.
Sold per 15-gram vial, which is about a zillion beads!
And see below (down below the artwork) for a quick pic on a cold Winter's day (you can, at least, see the size of the vial).