Information regarding U.S. coins and U.S. error coins.
You can diversify by investing in rare coins. Rare coins are a good hedge against inflation.
The price of coins is directly linked to price of bullion gold, silver, & cooper. The rare coins on the other hand is not effected dramatically by the change in price of precious metals. One reason being the rarity of the coin. Therefore, it is a very good liquid asset on hand vs money in bank or a house.