Troctolite 76535 is a lunar sample discovered and collected on the Apollo 17 mission in 1972 in the Taurus–Littrow valley. It has a mass of about 156 grams (5.5 oz) and is about 5 centimeters (2.0 in) across at its widest point. It was collected by geologist astronaut Harrison Schmitt as part of a "rake sample" of lunar soil at Geology Station 6, near the base of the North Massif.[1] Troctolite 76535 has been called the most interesting sample returned from the Moon.[2]
Troctolite 76535 is a coarse-grainedplutonic 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-plagioclase cumulate with a granular polygonal texture.[2] Olivine and plagioclase are of about equal quantities within 76535, while the remaining approximately 4% is made up of primarily orthopyroxene. According to early studies, the sample cooled at a depth of about 10–20 kilometers (6.2–12.4 mi), as well as its reequilibration and annealing.[3] Later work indicated that the rock formed at a depth of 47 kilometers,[4] about the middle to lower crust of the Moon,[5] Investigations have shown that the rock may have formed as a cumulate at depth, thus possibly making the sample an important link in the understanding of the geologic timeline of the Moon.[6]
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 or generated a core dynamo. The results of these studies have been shown to support the core dynamo hypothesis.[7]
^Schwartz, J. M.; McCallum, I. S. (1999). "Inferred Depths of Formation of Spinel Cataclasites and Troctolitic Granulite, 76535 Using New Thermodynamic Data for Cr-Spinel". Lunar and Planetary Science Conference: 1308. Bibcode:1999LPI....30.1308S.
