Pedantry: US Gold eagle coins are actually legal tender US currency with a $50 face value.

So while it would be exceedingly foolish to treat an ounce of gold like a $50 coin, you could.

Where this becomes slightly interesting is the $10k limit on foreign currency declarations in international travel ... since these are $50 coins of US legal tender, you should be able to travel with 199 of them (worth about $200k) without declaring anything.

YMMV. IANAL.