Moon rock or lunar rock is rock originating from Earth's Moon. This includes lunar material collected during the course of human exploration of the Moon, and rock that has been ejected naturally from the Moon's surface and landed on Earth as meteorites. Sources Moon rocks on Earth come from four sources: those collected by six United States Apollo program crewed lunar landings from 1969 to 1972; those collected by three Soviet uncrewed Luna probes in the 1970s; those collected by the Chinese Lunar Exploration Program's uncrewed probes; and rocks that were ejected naturally from the lunar surface before falling to Earth as lunar meteorites. Apollo program Six Apollo missions collected 2,200 samples of material weighing , processed into more than 110,000 individually cataloged samples. Luna program Three Luna spacecraft returned with of samples. The Soviet Union abandoned its attempts at a crewed lunar program in the 1970s, but succeeded in landing three robotic Luna spacecraft with the capability to collect and return small samples to Earth. A combined total of less than half a kilogram of material was returned. In 1993, three small rock fragments from Luna 16, weighing 200 mg, were sold for US$ 442,500 at Sotheby's (). In 2018, the same three Luna 16 rock fragments sold for US$ 855,000 at Sotheby's. Chang'e Chang'e 5, the fifth lunar exploration mission of the Chinese Lunar Exploration Program returned with ~ of samples. Lunar meteorites More than 370 lunar meteorites have been collected on Earth, representing more than 30 different meteorite finds (no falls), with a total mass of over . Some were discovered by scientific teams (such as ANSMET) searching for meteorites in Antarctica, with most of the remainder discovered by collectors in the desert regions of northern Africa and Oman. A Moon rock known as "NWA 12691", which weighs , was found in the Sahara Desert at the Algerian and Mauritanian borders in January 2017, and later went on sale for $2.5 million in 2020. Dating Rocks from the Moon have been measured by radiometric dating techniques. They range in age from about 3.16 billion years old for the basaltic samples derived from the lunar maria, up to about 4.44 billion years old for rocks derived from the highlands. Based on the age-dating technique of "crater counting," the youngest basaltic eruptions are believed to have occurred about 1.2 billion years ago, but scientists do not possess samples of