Yes. Cobalt forms many salts and some other compounds as well.
Cobalt react with oxygen, sulfur, fluorine, chlorine, carbon, nitrogen etc.
There is no reason at all why cobalt cannot be combined with more cobalt. It can. Cobalt is a metal. It can be recovered from ore and refined, then melted down with other cobalt pieces to form one large mass of the metal.
The noble gases.
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Hydrogen can react with practically all other elements.
Nitrogen react with the majority of other chemical elements.
Zinc is usually combined with other elements.
No. Pure cobalt is not found in nature, only in combination with other elements, and is therefore not considered a mineral, but a chemical element.
Elements form molecules of chemical compounds
Silicon can be combined with many elements forming chemical compounds as fluorides, chlorides, carbides, nitrides, etc.