Question

Is gold nugget a mineral and if not why?

Answer 1

A mineral does not have to be a compound, although the vast majority are.

You need to consider what comprises a mineral - a naturally occurring, inorganic, crystalline substance.

So let's break that down in the case of your gold nugget:

naturally occurring: yes

inorganic: yes

crystalline: Usually

So a gold nugget can be a mineral, as they are usually crystalline. Other examples of metals that are minerals are copper, silver and platinum, and they are usually called "native elements" if they exist as a metal in nature, rather than a compound

Answer 2

A mineral need not be crystalline. Silicates are classic examples.

Answer 3

Perhaps you mean it has to be in the solid state? Exempli gratia, you wouldn't ordinarily call F2, H2O2, or NH4 a "mineral?"