Prior to the Apollo missions, there were prominent scientists who disagreed about the origin of the moon; some predicted the rocks would look like common meteorites, indicating that the moon had always been a cold object out in space. Given the strong debate at the time, the actual nature of the rocks of the moon was a surprise. They were initially classified into four large groups: crystalline igneous rocks like basalt; crystalline igneous rocks, such as gabbros; breccias and microbreccias; and sands and soils. In this way more than thirty species of minerals in Moon rocks and four more in the remains of meteorites were identified.
Following the initial studies it was found that the most abundant minerals in all kinds of rock were pyroxenes, feldspars and ilmenite, a relatively rare oxide on Earth. Although some of the rocks from the moon had been broken up, they all had some things in common; they were originally formed as igneous rocks, from cooling of a hot moon through volcanic an intrusive processes similar to those on Earth. However, although most of the species identified are more or less generally common in terrestrial rocks, some were rare and a few were first discovered in Moon rocks.
The lunar maria, or seas, cover 16% of the surface and are of volcanic origin. Volcanoes were very active in the past although they no longer erupt today. The first crewed mission to the Moon, Apollo XI, landed in the sea of Tranquillity and collected samples of basalts, the predominant rock in lunar maria, as was confirmed by later missions. The basalts in the lunar maria contained titanium dioxide in varying concentrations.
Ilmenite is an oxide of titanium and iron that is relatively rare on Earth. However, it is the most abundant mineral on the Moon—between 10 and 18% of many rocks by weight. It is also the mineral with the largest crystals, with some being several millimetres long. Lunar ilmenite is very pure and many examples have an unusual high titanium content. Other common lunar oxides are chromite, spinel, rutile, baddeleyite, as well as some silica minerals: quartz, cristobalite and tridymite.
The lunar highlands cover the majority of the Moon’s surface and are coated with regolith, a layer of grey rock dust produced by countless meteorite impacts. Other kinds of rock predominate in this region, for example anorthosite consisting of plagioclases, olivines and pyroxenes; norite, a rock similar to gabbro but containing orthopyroxene; and troctolite, a rock consisting solely of anorthite-type calcic plagioclase and of olivine.
Apart from oxides and silicates, the most abundant basic components of lunar rocks, other unexpected minerals have also been identified. For example apatite and withlockite, both calcium phosphates, and aragonite, a carbonate, are just a few of the surprising substances found in samples. Native elements such as copper, tin and iron, were also found, together with sulphides such as troilite and pentlandite.
The astronaut Neil Armstrong, one of the crew members of the first mission, has had a mineral, armstrongite, dedicated to him. It is a hydrated cyclosilicate of calcium and zirconium with a momoclinic structure. However, armstrongite was not found in lunar rocks but was discovered in terrestrial granitic pegmatites.
~ JM
Image Credit: NASA/JPL sourced from https://www.nasa.gov/multimedia/imagegallery/image_feature_819.html
More Info:
Lunar Surface: https://www.nasa.gov/mission_pages/LRO/news/moon-zoo.html
Moon packed with precious titanium: http://bit.ly/1NBH6X8
Wu, Y., Zhang, X., Yan, B., Gan, F., Tang, Z., Xu, A., ... & Zou, Y. (2010). Global absorption center map of the mafic minerals on the Moon as viewed by CE-1 IIM data. Science China Physics, Mechanics and Astronomy, 53(12), 2160-2171
http://webmineral.com/
