"Bad guest" Cacoxenite returns as a fragile fluffball of translucent orange fibrous crystals with a silky sheen. Often associated with iron ores, it earns its nickname by weakening iron.

New competitor Charoite is such a striking purple, it was originally accused of using dye instead of manganese. This semiprecious gemstone is weakly fluorescent and slightly radioactive, subtly spicing up jewlery collections.

They're both beautiful with unusual shapes, but only one moves on to Round 2!

Voting for each match starts and ends at 06:00 GMT. Due to site limitations, the polls will continue to be visible until manually closed by volunteers, but only votes cast in the 24-hour period will be tallied.