Add a variation of thunder nights called meteor showers.
the symbol wouldn't be a colored night, but bright constellations around the sky that drop meteors instead of lightning strikes.

The meteors kill you on impact, and there's no way to stop them besides being in a shelter. If not it will break open and have a small chance to give a crystal

Crystals could be used as an efficient fuel source, a special crafting resource, or a weaker version of a crucifix that can be thrown and summon a smaller meteor shower.