Geologist Mike Bowers told the Daily Mail that the agate, discovered in November in the Rio Grande dol sul region of Brazil, could be worth as much as $10,000.
"I think this is probably the most perfect Cookie Monster out there," said Bowers to the Mail. "I have seen others but here you have it complete (both sides) Lucas Fassari is actually the one who found it."
"This is very unusual!" added Bowers. "There are a few famous agates out there: the owl, the scared face... there are many approximate ones but rare to find clear well defined like that."
The International Gem Society (IGS) defines agate as a "variety of chalcedony, a cryptocrystalline form of quartz. Translucency, patterns of color, or moss-like inclusions may distinguish this stone from other forms of chalcedony. Agates can show a wide variety of vivid, multiple colors."
Chalcedony is a "mixture of microcrystalline or cryptocrystalline quartz and moganite," according to the IGS.