Located on the far side of the moon and undetected until a space probe measured its odd mineralogy, the rocks are located in a few isolated deposits, ScienceNews.org reported Wednesday.
"These are very unusual areas," Carle Pieters, a planetary geologist at Brown University, told a meeting of the Geological Society of America Tuesday.
Pieters calls the new rock type OOS because it is rich in the minerals orthopyroxene, olivine and spinel.
The spinel, a gemstone prized on Earth, is particularly intriguing, scientists say, as it occurs only in the smallest trace amounts in every other part of the moon.
How the OOS material got where it is remains something of a mystery.
Most scientists think the moon formed when a Mars-sized object hit the infant Earth 4.5 billion years ago, knocking a large amount of material into Earth orbit where it cooled and solidified to form the moon.
The newly identified, spinel-rich areas could be from those early days, Pieters says, part of the moon that cooled early on deep in the crust and later came to the surface through some kind of geologic action.