KREEP

KREEP is an acronym used in geochemistry to represent a mixture of K-potassium, REE-rare earth elements, and P-phosphorus. Many scientists believe that this component of lunar rocks is the remnant of a magma ocean which is widely believed to have covered the moon after it formed in a cataclysmic collision between earth and another body approximately 4.5 billion years ago.

KREEP is a composite of what scientists term "incompatible elements": elements which cannot fit into the crystal structures formed by cooling magma and are left floating on the surface. It is considered a convenient tracer for researchers seeking to chronicle the volcanic history of the lunar surface, as well as impacts of celestial bodies.