Moonstone
adularia — light that walks
The glow that moves across a moonstone — adularescence — is light scattering between feldspar layers finer than a wavelength. Rome believed the stone was moonlight made solid and that it waxed and waned with the sky. Two thousand years later it is still the June birthstone, and the glow still walks.
“Born of the moon’s own beams, and it waxes with her.”Roman lore · Pliny’s era