There are many other asset classes out there with their own unique tax rules. For instance, futures contracts, options on futures, options on broad-based indexes, and collectables (which includes metals like gold) are subject to a special tax treatment.
Derivative contracts like futures contracts, options on futures, or options on broad-based indexes, are subject to Internal Revenue Code section 1256 (a.k.a 1256 contracts). These types of assets get special tax treatment called the 60/40 rule, where 60% of gains are taxed at the lower long-term capital gains rate and 40% at the ordinary income tax rate. In addition, if you hold section 1256 contracts, they're subject to the mark-to-market rule. If you hold these assets through the end of a calendar year, you'll have to recognize an unrealized gain or loss based on the fair market value on December 31.
Gains from the sale of collectibles, such as art, antiques, coins, and precious metals, are subject to a higher long-term capital gains tax rate of 28%. Whereas shorter-term gains on collectables are taxed at the ordinary income tax rates.