"Mona" could be a person's name, maybe a place. "Onyx" is a type of gemstone, but also an onyx stone is a mineral. Sudan is a country in Africa. So perhaps there's a location in Sudan named Mona that has onyx? Or maybe it's a fictional place combining these elements. Alternatively, the user might have misspelled something like "Mona Lisa" or "Monsoon Sudan," but that seems unlikely.