Hey jm,
Good question. Unfortunately, and as far as I know, gold and silver bullion including coins are considered collectibles in the US, same as art, stamps, antiques, and a whole lot more, and any profits, minus expenses, etc., are taxed at least at 28% in the US, if held more than a year. Less than a year taxed at personal tax rate, I think.
Fortunately, gold and silver mining stocks as well as other mining stocks are not considered collectibles and profits are taxed at the 15% long-term rate and personal tax rate if sold short-term.
Can be confusing and the rules debatable, but holding bullion or coins presents a potential future headache at selling time.