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.