The boulder is so exceptional, scientists have said it’s in a league of its own. Closer analysis with the rover’s instruments shows it is likely an anorthosite, a rock type never seen before while exploring Mars, Stack Morgan said, though there have been signs such rocks should exist. Not even the Curiosity rover, which has observed more variety in Gale Crater, has seen one quite like this.

Though such anorthosite rocks are on the moon and in mountain ranges on Earth, they’re generally considered rare in the solar system. True Martian examples have eluded researchers, including within our planet’s inventory of Red Planet meteorites that traveled through space to get here.

This discovery could bolster the idea that Mars’ early crust was way more complex than once thought — and perhaps similar to Earth’s original crust.