I always (possible naively) thought that elements are either natural or synthetic, either one or the other. But, according to the Wikipedia page about Synthetic Elements, it states that:
All elements with atomic numbers 1 through 98 are naturally occurring at least in trace quantities, but the following elements are usually produced through synthesis. Except for Francium, they were all discovered through synthesis before being found in nature.
These are shown in pink in the image below:
I understand that the amounts of these elements exist naturally in trace quantities, not necessarily on Earth, for example, according to the Jefferson Lab page about promethium:
Promethium does not occur naturally on earth, although it has been detected in the spectrum of a star in the constellation Andromeda.
This leads me to my question:
Is there a natural abundance threshold of a 'synthetic' element for it to be considered natural?