Book 27, Question 140
What can crystals tell us about other planets?
Mars rovers have found crystals that are clues to the planet's past.
Curiosity found veins of gypsum, a mineral that forms in water. Opportunity found little round pieces of hematite nicknamed blueberries, which also grew in watery places. Seeing these crystals tells scientists that liquid water once soaked the Martian ground. Crystals are like fingerprints for the places they grew.