Moqui marbles are also naturally occurring spheres, or so it is assumed, they are hematite surrounding compact sandstone.
Nobody is exactly sure how nature formed them but in the absence of other evidence, it is assumed they are natural.
"Nobody is exactly sure how nature formed them but in the absence of other evidence, it is assumed they are natural"
Kinda like the martian blueberries. No one who can be taken seriously thinks they were produced artificially but Mars is covered with them none the less.