Moon rock
Moon rock or lunar rock is rock that is found on the Earth's Moon including lunar material collected during the course of human exploration of the Moon, or rock that has been ejected naturally from the Moon's surface.
Luna mission sample returns
The Soviet Union attempted, but failed to make crewed lunar landings in the 1970s, but they 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.
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 these lavas. In contrast, the oldest ages of rocks from the Earth are between 3.8 and 4.28 billion years old.Composition
| Mineral | Elements | Lunar rock appearance |
| Plagioclase feldspar | Calcium Aluminium Silicon Oxygen | White to transparent gray; usually as elongated grains. |
| Pyroxene | Iron , Magnesium Calcium Silicon Oxygen | Maroon to black; the grains appear more elongated in the maria and more square in the highlands. |
| Olivine | Iron Magnesium Silicon Oxygen | Greenish color; generally, it appears in a rounded shape. |
| Ilmenite | Iron , Titanium Oxygen | Black, elongated square crystals. |
Moon rocks fall into two main categories: those found in the lunar highlands, and those in the maria. The terrae consist dominantly of mafic plutonic rocks. Regolith breccias with similar protoliths are also common. Mare basalts come in three distinct series in direct relation to their titanium content: high-Ti basalts, low-Ti basalts, and Very Low-Ti basalts.
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.
Highlands rocks
| Plagioclase | Pyroxene | Olivine | Ilmenite | |
| Anorthosite | 90% | 5% | 5% | 0% |
| Norite | 60% | 35% | 5% | 0% |
| Troctolite | 60% | 5% | 35% | 0% |
Primary igneous rocks in the lunar highlands compose three distinct groups: the ferroan anorthosite suite, the magnesian suite, and the alkali suite.
Lunar breccias, formed largely by the immense basin-forming impacts, are dominantly composed of highland lithologies because most mare basalts post-date basin formation.
- The ferroan anorthosite suite consists almost exclusively of the rock anorthosite with less common anorthositic gabbro. The ferroan anorthosite suite is the most common group in the highlands, and is inferred to represent plagioclase flotation cumulates of the lunar magma ocean, with interstitial mafic phases formed from trapped interstitial melt or rafted upwards with the more abundant plagioclase framework. The plagioclase is extremely calcic by terrestrial standards, with molar anorthite contents of 94-96%. This reflects the extreme depletion of the bulk Moon in alkalis as well as water and other volatile elements. In contrast, the mafic minerals in this suite have low Mg/Fe ratios that are inconsistent with calcic plagioclase compositions. Ferroan anorthosites have been dated using the internal isochron method at "circa" 4.4 Ga.
- The magnesian suite consists of dunites, troctolites, and gabbros with relatively high Mg/Fe ratios in the mafic minerals and a range of plagioclase compositions that are still generally calcic. These rocks represent later intrusions into the highlands crust at round 4.3-4.1 Ga. An interesting aspect of this suite is that analysis of the trace element content of plagioclase and pyroxene require equilibrium with a KREEP-rich magma, despite the refractory major element contents.
- The alkali suite is so-called because of its high alkali content—for Moon rocks. The alkali suite consists of alkali anorthosites with relatively sodic plagioclase, norites, and gabbronorites with similar plagioclase compositions and mafic minerals more iron-rich than the magnesian suite. The trace element contents of these minerals also indicates a KREEP-rich parent magma. The alkali suite spans an age range similar to the magnesian suite.
- Lunar granites are relatively rare rocks that include diorites, monzodiorites, and granophyres. They consist of quartz, plagioclase, orthoclase or alkali feldspar, rare mafics, and rare zircon. The alkali feldspar may have unusual compositions unlike any terrestrial feldspar, and they are often Ba-rich. These rocks apparently form by the extreme fractional crystallization of magnesian suite or alkali suite magmas, although liquid immiscibility may also play a role. U-Pb date of zircons from these rocks and from lunar soils have ages of 4.1-4.4 Ga, more or less the same as the magnesian suite and alkali suite rocks. In the 1960s, NASA researcher John A. O'Keefe and others linked lunar granites with tektites found on Earth although many researchers refuted these claims. According to one study, a portion of lunar sample 12013 has a chemistry that closely resembles javanite tektites found on Earth.
- Lunar breccias range from glassy vitrophyre melt rocks, to glass-rich breccia, to regolith breccias. The vitrophyres are dominantly glassy rocks that represent impact melt sheets that fill large impact structures. They contain few clasts of the target lithology, which is largely melted by the impact. Glassy breccias form from impact melt that exit the crater and entrain large volumes of crushed ejecta. It may contain abundant clasts that reflect the range of lithologies in the target region, sitting in a matrix of mineral fragments plus glass that welds it all together. Some of the clasts in these breccias are pieces of older breccias, documenting a repeated history of impact brecciation, cooling, and impact. Regolith breccias resemble the glassy breccias but have little or no glass to weld them together. As noted above, the basin-forming impacts responsible for these breccias pre-date almost all mare basalt volcanism, so clasts of mare basalt are very rare. When found, these clasts represent the earliest phase of mare basalt volcanism preserved.
Mare basalts
- KREEP Basalts have extraordinary potassium content. These contain 13-16 percent Al2O3, 9-15 percent FeO, and are enriched in magnesium and incompatible elements 100-150 times compared to ordinary chondrite meteorites. These are commonly encountered around the Oceanus Procellarum, and are identified in remote sensing by their high thorium contents. Most of incompatible elements in KREEP basalts are incorporated in the grains of the phosphate minerals apatite and merrillite.
Curation and availability
The main repository for the Apollo Moon rocks is the Lunar Sample Laboratory Facility at the Lyndon B. Johnson Space Center in Houston, Texas. For safe keeping, there is also a smaller collection stored at White Sands Test Facility in Las Cruces, New Mexico. Most of the rocks are stored in nitrogen to keep them free of moisture. They are handled only indirectly, using special tools. Some Moon rocks from the Apollo missions are displayed in museums, and a few allow visitors to touch them. One of these, called the Touch Rock, is displayed in the Smithsonian National Air and Space Museum in Washington, D.C. The idea of touchable Moon rocks at a museum was suggested by Apollo scientist Farouk El-Baz, inspired his childhood pilgimage to Mecca where he touched the Black Stone. Moon rocks collected during the course of lunar exploration are currently considered priceless. In 2002, a safe was stolen from the Lunar Sample Building that contained minute samples of lunar and Martian material. The samples were recovered, and NASA estimated their value during the ensuing court case at about $1 million for 10 oz. of material. Naturally transported Moon rocks in the form of lunar meteorites are sold and traded among private collectors. Goodwill Moon rocksApollo 17 astronauts Eugene Cernan and Harrison Schmitt picked up a rock "composed of many fragments, of many sizes, and many shapes, probably from all parts of the Moon". This rock was later labeled sample 70017. President Nixon ordered that fragments of that rock should be distributed in 1973 to all 50 US states and 135 foreign heads of state. The fragments were presented encased in an acrylic sphere, mounted on a wood plaque which included the recipients' flag which had also flown aboard Apollo 17. Many of the presentation Moon rocks are now unaccounted for, having been stolen or lost.DiscoveriesThree minerals were discovered from the Moon: armalcolite, tranquillityite, and pyroxferroite. Armalcolite was named for the three astronauts on the Apollo 11 mission: Armstrong, Aldrin and Collins.Stolen and missing Moon rocksBecause of their rarity on Earth, and the difficulty of obtaining more, Moon rocks have been frequent targets of theft and vandalism, and many have gone missing or were stolen.Image gallery |