Moonrocks

Moonrocks

Moon rock describes rock that formed on the Earth's moon. The term is also loosely applied to other lunar materials collected during the course of human exploration of the Moon.

Rocks collected 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 4.5 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 these lavas. In contrast, the oldest ages of rocks from the Earth are between 3.8 and 4.28 billion years old.

There are currently three sources of Moon rocks on Earth: 1) those collected by US Apollo missions; 2) samples returned by the Soviet Union Luna missions; and 3) rocks that were ejected naturally from the lunar surface by cratering events and subsequently fell to Earth as lunar meteorites. During the six Apollo surface excursions, 2,415 samples weighing 382 kg (842 lb) were collected, the majority by Apollo 15, 16, and 17. The three Luna spacecraft returned with an additional 0.32 kg (0.7 lb) of samples. Since 1980, over 120 lunar meteorites representing about 60 different meteorite fall events (none witnessed) have been collected on Earth, with a total mass of over 48 kg (105.8 lb). About one third of these were discovered by US and Japanese teams searching for Antarctic meteorites (e.g., ANSMET), with most of the remainder having been discovered by collectors in the desert regions of northern Africa and Oman.

Almost all lunar rocks are depleted in volatiles and are completely lacking in hydrated minerals common in Earth rocks. In some regards, lunar rocks are closely related to Earth's rocks in their isotopic composition of the element oxygen. The Apollo moon rocks were collected using a variety of tools, including hammers, rakes, scoops, tongs, and core tubes. Most were photographed prior to collection to record the condition in which they were found. They were placed inside sample bags and then a Special Environmental Sample Container for return to the Earth to protect them from contamination. In contrast to the Earth, large portions of the lunar crust appear to be composed of rocks with high concentrations of the mineral anorthite. The mare basalts have relatively high iron values. Furthermore, some of the mare basalts have very high levels of titanium (in the form of ilmenite).