A tiny Swiss gold coin bearing a picture of Albert Einstein sticking his tongue out has been crowned as the world's smallest commemorative coin, Switzerland's mint announced Tuesday.

The miniature coin, with a face value of a quarter of a Swiss franc (27 US cents, 23 euro cents), measures just 2.96 millimetres (0.1 inches) in diameter and weighs only 0.063 grammes (0.002 ounces).

"Guinness World Records has recognised the quarter-franc gold coin issued in 2020 as the world's smallest commemorative coin," Swissmint said in a statement.

Claiming inspiration from the "determination and patience" of theoretical physicist Einstein, who died in 1955, the coin features the Swiss citizen in his famous pose on the obverse.

The reverse shows the nominal value of the coin, the Swiss cross and the inscription Helvetia -- the Latin name for Switzerland, which is used on coins in the four-language European nation.

However, casual observers should not expect to see much.

The images on the world's smallest commemorative coin are too small to see with the naked eye
The images on the world's smallest commemorative coin are too small to see with the naked eye Swissmint / Handout

"The world's smallest commemorative coin is decorated with images that cannot be discerned with the naked eye. Swissmint has therefore designed special packaging, complete with magnifying lenses and light," it said.

Only 999 coins were struck, which all sold out quickly.

Meanwhile Switzerland also claimed another numismatic world record for the oldest coin still in circulation.

The 10-centime coin minted in 1879 remains valid as legal tender.

The coin's reverse side features the face value surrounded by a wreath of oak leaves.

The obverse features a woman's head in profile, looking to the right and wearing a diadem.

"The unaltered 10-centime coin has thus been in use for over 140 years, and has now been recognised by Guinness World Records as the world's oldest coin still in circulation," said Swissmint.