lead
It is very hard to find in nature. Tritium is a very rare isotope form of hydrogen, the only radioactive form of this widespread element.
An element occur in nature as a pure element or as a compound.
Berkelium is a very rare, artificial element, impossible to found in the nature.
Astatine exist in nature very probable as compounds.
Neptunium has not minerals. It is an artificial element and in the nature is very rare, in some uranium ores.
Yes, Helium is a element. It is inert in nature.
Gold is a beautiful metal, practically unreactive, exist in nature as a pure element, is expensive and very desirable.
Gold is a very unreactive element, so it occurs as gold metal in nature. However, aluminum is more reactive, and so it occurs in aluminum ore (aluminum oxide) in nature, not as aluminum metal.
Bromine is a liquid but doesn't occur in nature as a free element.
An element is an element, whether it is found in nature or created in a lab.
The element my be rare because it is part of a compound and cannot be found as an element as itself in nature. The only way to get the element is to extract it from the compound. That may not be very easy.
Fluorine is an element that is never found in its free state in nature due to its high reactivity, forming compounds with other elements very quickly.