Retired Royal Observatory engineer Mr Sheffield (right) is one of a handful of people in possession of samples of moon dust from the famous 1969 Apollo 11 space mission.
History-making astronaut Neil Armstrong had inadvertently brought the moon dust back with him from the Sea of Tranquility on the back of a magazine.
It was picked up by NASA photo technician Terry Slezak, who was subsequently contaminated and had to join the crew of the space ship in quarantine.
They gave Slezak a montage of photos from the expedition, held together by sticky tape covered in moon dust from the magazine, and he sold it to a German dealer for £14,000.
The dealer then cut the original sample down into 50 smaller units, including the one held by Mr Sheffield, each valued at more than £2,000.
He also owns a second, larger sample, of moon dust from the 1971 Apollo 15 landings, and claims to be the only person in Scotland to have two samples from two different space missions.
Although they are little more than a pinhead in size and were legally purchased by 62-year-old Mr Sheffield, who lives near Haddington, ownership of the samples has been contested by NASA, which claims them as a national treasure for the United States.
They are kept in a safe at Mr Sheffield's secluded home, along with provenance documents confirming their authenticity.
"I have had various approaches from NASA over the years asking me to return the samples, but I have always said no," he said.
"I bought them legally and am thrilled to have the experience of being able to touch a piece of the moon.
"We have kind of reached a stalemate, in that I have been led to understand that NASA will not pursue the matter unless I put them on public display, which I have no intention of doing.
"As long as I keep them safe and secure I don't think they will give me any bother."
Although only smudges of the moon dust can be seen with the naked eye, Mr Sheffield has created extensive accompanying photographs of increasing enlargements, which show the details of the samples - including the unique glass beads that make up much of the lunar surface dust.
In the US, it is illegal to own (or try to own) NASA moon samples. NASA stores the bulk of the moon rocks and keeps an eye on other samples which were loaned to foreign governments and various other organisations.
Any attempted sale of such items is investigated by NASA. In the case of small traces of moondust, however, if they were sourced from a legally sold artifact, such as is the case with the samples held by Mr Sheffield, then the space agency can turn a blind eye.