[RD (OP)]

Minute quantities of the fullerenes, in the form of C60, C70, C76, C82 and C84 molecules, are produced in nature, hidden in soot and formed by lightning discharges in the atmosphere

https://en.wikipedia.org/wiki/Fullerene

Can endohedral-fullerenes be found occurring naturally on surface of the Earth, or are they exclusively a man-made substance ?

[evan_au]

There is a maxim about the universe which I always tell my students: That which is not explicitly forbidden is guaranteed to occur.

Reading how endohedral-fullerenes are formed in the laboratory - it is effectively an artificial lightning strike, which produces a huge variety of random compounds from the debris, from which they refine the compounds of interest.

I imagine that natural lightning strikes produce a similar debris field, some of which must be endohedral-fullerenes. It's just that they are spread so thinly in nature that it is impractical to find them.

The spectral signature of "Buckyballs" has also been discovered in deep space; some of these fullerenes must contain other atoms.

[RD (OP)]

The spectral signature of "Buckyballs" has also been discovered in deep space; some of these fullerenes must contain other atoms.

Apparently found in meteorites ...

... fullerenes extracted from the Allende and Murchison meteorites contained endohedral helium ...

http://www.sciencedirect.com/science/article/pii/S1044030502006505#BIB24