A moon rock is a piece of rock or soil collected from the Moon's surface and brought back to Earth. Between 1969 and 1972, American astronauts on the Apollo missions gathered 842 pounds of moon rocks, carefully packing them in special containers for the journey home. Soviet robotic missions also returned smaller samples.

These rocks are tremendously valuable to scientists because they reveal the Moon's history and formation. Moon rocks contain no water and no fossils, since the Moon has never had life. They're made of minerals similar to Earth rocks but with important differences that tell us the Moon formed about 4.5 billion years ago, possibly when a Mars-sized object crashed into the early Earth.

Most moon rocks stay locked in NASA laboratories, where scientists from around the world study tiny samples. A few pieces tour museums in special cases so people can see them. Some countries received small moon rocks as gifts from the United States. Because they're so rare and scientifically important, moon rocks are worth more per ounce than gold, diamonds, or almost any other material on Earth.

The term can also refer to rocks on the Moon that astronauts photographed but didn't bring home.