Have you ever heard about error coins?

Simply put, an error coin is a mint-made mistake -- in the process of creating the coin at the U.S. mint, some sort of mistake was made affecting the "look" of the coin itself.

There are many types of error coins, and the exciting thing about error coins is that they can often be be found in circulation. Here's the kicker: error coins are often worth hundreds and even thousands of dollars!

One of the most interesting varieties the U.S. Mint created over its decades of producing Lincoln cents came in 1943. That's when the Mint, pursuant to 1942's Public Law 815, temporarily suspended use of copper in pennies to ration the metal for use in war materials.

Thus, 1943 Lincoln cents were struck with a steel core which was coated with a thin plating of zinc. Zinc, by the way, is currently used in the core of all Lincoln cents struck since 1982. These steel pennies have a weight of 2.70 grams, as opposed to 3.11 grams for typical copper pennies.

Steel pennies generally have a white top silvery appearance, though many have corroded over the years. It is also common to find some worn steel cents with rust, or in colors ranging from black to gray.

Ah, rare coins... we all would love to find one in an attic chest, our inheritance or, yes, even our pocket change. In fact, none of these scenarios are impossible.

You may be glad to hear that there are dozens of U.S. coins considered rare, and that many estates include rare U.S. coins. Many others are found in attics, old drawers and chests, and some are even found in circulation!

So, how do you know if a coin you have is rare? And how do you find out how much your rare coin is worth?

Wheat pennies have been a popular coin to "snag" out of circulation ever since the Memorial design on the reverse of the Lincoln penny replaced the two wheat stalks in 1959.

While wheat pennies are getting increasingly hard to find with each passing year, they are still located in pocket change occasionally, and many people have wheat pennies by the hundreds -- and even thousands -- in penny jars, clothes drawers, attic boxes, and coin collections.

In general, most wheat pennies are worth only a few cents (perhaps 10 cents) if worn and of a highly common date and mint mark combination. However, many are quite valuable. In fact, some of the scarcest wheat cents are downright expensive -- costing into the hundreds of dollars in the most worn condition.

Those collecting coins from pocket change are probably wondering:

What kinds of coins can I find in circulation?

While it is theoretically possible to find any legal tender coin in circulation, including old and even rare issues, the likelihood of finding such coins in your pocket change is small (but not impossible).

This brings us to remember that the grand majority of the coins to be found in circulation today are primarily from among the cent, nickel, dime, and quarter denominations, and are usually coins struck from sometime during the last few decades.

Half-dollars have not been regularly seen in circulation in many years (but can be found at banks), and dollar coins have yet to reach their circulation potential -- many can be found at banks, some stores, and certain vending machines which operate for transit authorities and the U.S. Postal Service.

The Buffalo nickel -- the design of the United States' 5-cent coin from 1913 to 193 -- remains one of the most popular and well-loved coins.

This, despite the fact that it has been nearly a century since Buffalo nickels first appeared in the pockets and purses of Americans.

Here's everything you want to know about Buffalo nickels and what they're worth today.

I have been a coin collector for many years and have learned a lot through my day-to-day experiences in the hobby. But I sure would not be as knowledgeable in my field if not for reading some terrific books about the pastime I love.

A trip to the bookstore, library, coin dealer, or Amazon.com will give you a choice of dozens of prominent coin books, all of them great in their own right.

Here are 5 books I believe every coin collector should consider buying...

Do you know what a proof coin is?

Are you wondering how to tell if a coin is proof grade or not?

"Proof," in fact, does not refer to a particular grade. Rather, "proof" refers to the result when a coin is manufactured in a special way.

Proof coins represent the finest, the very best, that any U.S. Mint has to offer in terms of quality, care, and attention to detail when it comes to producing a coin.

World War II caused the United States and its citizens to ration certain materials with the purpose of keeping around important resources for winning the war. The United States Treasury and the U.S. Mint followed suit.

While most people are aware of the steel Lincoln pennies which were produced in 1943, fewer seem to know that the Jefferson silver nickels also spent a short period of time being produced under a special composition issue.

With nickel an important military material, the United States Congress required the U.S. Mint to begin striking nickels from a composition of copper (56%), silver (35%), and manganese (9%).

Here's more about those silver Jefferson "wartime" nickels.

Among the most popular U.S. coins are Lincoln wheat pennies. Millions collect them, and they have been highly popular with coin collectors of all ages and incomes for decades.

But which are the rarest wheat pennies? And what are the low-ball pricing figures for these rare Lincoln wheat cents?

Let's examine these 7 rare wheat pennies closer.