Unusual minerals in impact craters on the moon may not have originated on the moon, but may be from asteroids that created the craters a U.S. researcher says.

The minerals were once thought to be representative of the lunar interior. Scientists trying to determine what the moon is made of will have to take into account they may not be indigenous to the moon, Jay Melosh of Purdue University said.

"Future studies of the moon's composition will have to show that exposed surface rocks really come from the moon and were not delivered by impacts, especially for unusual or exotic minerals," he said.

Melosh, with colleagues from Purdue and the Chinese Academy of Sciences in Beijing, used computer models to simulate the formation of lunar craters by asteroid impacts and found in some impacts much of the asteroid's material is not vaporized but is instead deposited in the center of the impact craters.

That means minerals scientists had assumed were exhumed from beneath the lunar surface by the impacts were actually delivered from space as part of the asteroids, the researchers said.

"We cannot infer the deep composition of the moon from rocks in the centers of large craters without more care than has been used to date," Melosh told Space.com.

The study has been published in the journal Nature Geoscience.