Apollo 11, the first manned craft to land on the Moon, brought back 22 Kg of lunar samples, including 50 rocks. Two main types of rock were determined, basalts and breccias.
Basalts are formed when molten lava solidifies, and are dark grey in color, which gives the dark areas of the Moon its appearance in the night sky when viewed from Earth. Although similar to terrestrial basalt, lunar basalt contains more of the element titanium.
Breccias are composed of the fragments of older rocks, formed from meteoric impact upon the lunar surface.
Later Apollo missions uncovered a few variant rock samples of these two main classes. Within the last few years, researchers found traces of water within the basalts. At the time of Apollo 11's return to Earth, the instruments used for detection weren't as sensitive, and they concluded that the Moon was arid.