A rock on Mars spilled a surprising yellow treasure after Curiosity accidentally cracked through its unremarkable exterior.

When the rover rolled its 899-kilogram (1,982-pound) body over the rock back in May, the rock broke open, revealing yellow crystals of elemental sulfur: brimstone.

Although sulfates are fairly common on Mars, this represents the first time sulfur has been found on the red planet in its pure elemental form.