The Moon Guide
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U. S. N. O.
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The phase of the Moon right now

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Colour-enhanced view of the lunar surface from the Galileo spacecraft
What is the Moon made of?

Contrary to popular belief the Moon is not made of cheese! It is made up of many different types of rocks, many of which have been broken up and formed back together again and again because of the numerous impacts that have occurred over the Moon’s 4.6 billion year lifetime. These types of rocks are known as breccias.

The compositions of the different rock types are related to the colours of the rocks that make up the highlands and the maria. The most common type of Moon rock is the light coloured anorthosite, which contains a lot of the mineral feldspar, and makes up the rugged lunar highlands. It is also the most common type of rock on the Earth. The sheer amount of anorthosite on the Moon tells geologists that the Moon was entirely molten at some point in its history because the feldspar crystals that began to crystallise out of the melt were less dense than the melt itself, and so floated to the top of this molten ‘magma ocean’, eventually solidifying into an almost entirely feldspar crust.

Another type of highlands rock is similar to anorthosite but contains some other minerals, like olivine, which is rich in magnesium. This rock group is called the Mg-suite. KREEP makes up the rest of the highlands rock and stands for potassium (chemical symbol K), rare earth elements (REE) and phosphorous (P). These chemical elements do not mix with the other rock forming minerals of plagioclase feldspar, pyroxene and olive, so they get left behind in the melt while everything else crystallises. Rocks formed from this left-over melt has unusual mineral compositions, which helps geologists learn about the final stages of the Moon’s geologic evolution.

Basalt is the main component of the lunar maria. Basalt also makes up a large component of Earth and Moon rocks, forming from solidified lava, and is made up of the minerals pyroxene and plagioclase feldspar, sometimes with a bit of olivine. The basalts were erupted into giant impact basins several hundred of thousands of years after the impact event.

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Lunar geologist

Lunar geology

Moon rocks on Earth

Moon quakes

How the Moon was formed

Geology of the Moon's features

What is the Moon made of?

Lunar gardening

About impacts

Ray craters

Ageing wrinkles

Meandering channels

 
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