Actually, Moon rocks and Earth rocks are quite similar, as long as we keep in mind a few important differences. With the exception of the possibility that there may be water ice at the poles of the Moon in craters that are permanently shadowed from the Sun's rays, there is virtually no water on the Moon-not running across the surface, not in the rocks. This eliminates a whole class of rocks found on Earth, the sedimentary rocks, that are formed by deposition or precipitation in water. There are no sandstones or limestones on the Moon!

The chemistry of lunar rocks is similar to Earth rocks, but lunar rocks tend to be depleted in what is known as volatile elements, like sodium or potassium, elements that evaporate at lower temperatures. Many lunar basalts are higher in titanium than Earth basalts.