This rock is made of fragments of other rocks that were broken by collisions of meteorites with the Moon. The fragments were heated by the collisions that broke them apart, so that sharp edges melted and stuck to other grains to form a new rock, composed entirely of broken rocks and smaller mineral grains, called a breccia (breck’sha).
Breccias like this one were produced when the original crust of the Moon was completely broken up by meteorite impacts. Pieces of this crust now exist as rock fragments in these breccias, and for this reason many of the larger fragments (about 1 cm or 0.4 inches across) are subjects of intense study by several of the 100 scientific laboratories throughout the world working with lunar samples.
The chip in this disk weighs about 1 gram and was removed from rock number 15059, which weighed 1149 grams (2.5 lbs.). The Apollo 15 astronauts collected this rock, which was lying loose on the surface, near the canyon, Hadley Rille. The rock was part of a layer of breccia and evidently was cast out of the crater when it was formed by a meteorite.