Samples of moon dust gathered by the first men to walk on the moon and missing for more than 40 years have been found in a California warehouse, officials said.

NASA sent 68 grams of lunar dust collected by Neil Armstrong and Buzz Aldrin during the Apollo 11 moon landing to the University of California, Berkeley, in 1969 to be studied by Melvin Calvin, who had won the 1961 Nobel prize in chemistry.

After being studied for carbon compounds by Calvin and his colleagues, the samples were prepared to be sent back to NASA but only 50 grams were returned.

The remainder was thought to have been destroyed in the process of research until 3 grams of the dust were discovered in in April a warehouse at the Lawrence Berkeley National Laboratory.

Archivist Karen Nelson uncovered the moon dust -- about 20 vials with handwritten labels dated "24 July 1970" -- while reviewing and clearing out artifacts from the facility's warehouse, a Berkeley Lab release reported.

The lost samples have been returned to NASA's Lyndon B. Johnson Space Center in Houston, where they may still be "scientifically useful," curator Ryan Ziegler was quoted as saying.

Ziegler said he believed there was no ulterior motive in the misplacement of the moon dust samples.

"I have a feeling [Calvin] just forgot about them," he said.