Troctolite 76535 is a

lunar sample 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 ...

discovered and collected on the

Apollo 17 Apollo 17 (December 7–19, 1972) was the final mission of NASA's Apollo program, the most recent time humans have set foot on the Moon or traveled beyond low Earth orbit. Commander Gene Cernan and Lunar Module Pilot Harrison Schmitt walked on ...

mission in 1972 in the

Taurus–Littrow valley Taurus–Littrow is a lunar valley located on the near side at the coordinates . It served as the landing site for the American Apollo 17 mission in December 1972, the last crewed mission to the Moon. The valley is located on the southeastern ...

. It has a mass of about and is about across at its widest point. It was collected by geologist astronaut

Harrison Schmitt Harrison Hagan Schmitt (born July 3, 1935) is an American geologist, retired NASA astronaut, university professor, former U.S. senator from New Mexico, and the most recent living person—and only person without a background in military aviation ...

as part of a "rake sample" of lunar soil at Geology Station 6, near the base of the North Massif. Troctolite 76535 has been called the most interesting sample returned from the Moon.

Description

Troctolite Troctolite (from Greek τρώκτης 'trout' and λίθος 'stone') is a mafic intrusive rock type. It consists essentially of major but variable amounts of olivine and calcic plagioclase along with minor pyroxene. It is an olivine-rich anorth ...

76535 is a

coarse-grained Granularity (also called graininess), the condition of existing in granules or grains, refers to the extent to which a material or system is composed of distinguishable pieces. It can either refer to the extent to which a larger entity is subd ...

plutonic Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form '' intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: March ...

rock that is believed to have had a slow cooling history. The rock originates from early in the Moon's history. Geologists have described it as a coarse-grained

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...

plagioclase Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more prope ...

cumulate with a granular polygonal texture. Olivine and plagioclase are of about equal quantities within 76535, while the remaining approximately 4% is made up of primarily

orthopyroxene The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...

. According to early studies, the sample cooled at a depth of about , as well as its reequilibration and annealing. Later work indicated that the rock formed at a depth of 47 kilometers, about the middle to lower crust of the Moon, Investigations have shown that the rock may have formed as a

cumulate Cumulate rocks are igneous rocks formed by the accumulation of crystals from a magma either by settling or floating. Cumulate rocks are named according to their texture; cumulate texture is diagnostic of the conditions of formation of this group o ...

at depth, thus possibly making the sample an important link in the understanding of the geologic timeline of the Moon. As Troctolite 76535 is the oldest known unshocked lunar rock, it has been used for thermochronological calculations in order to determine whether the Moon formed a metallic

core Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the central ...

or generated a core dynamo. The results of these studies have been shown to support the core dynamo hypothesis.

References

{{Apollo program Plutonic rocks Lunar science Lunar samples Apollo 17 Harrison Schmitt