They can be used to make jewelry, to make your bath more pleasant or, apocryphally, to buy an island.

I am a clock that hates the dark, dependent on the sunlight’s mark.

I am a boundary with no wall, A door with no hinges, A keeper of light and secrets. When I part, another world appears.

I guard my treasures deep in stone, A golden mask upon my throne. Though dead for centuries, I still reign, Beside the Nile's eternal plain.

Its yellow and it sometimes has holes in it.