Coal veins are typically found in sedimentary rock formations, particularly those that were formed during the Carboniferous period, which occurred roughly 300 million years ago. During this period, the Earth experienced lush vegetation and swampy conditions, which led to the accumulation of plant matter that eventually transformed into coal.

Specific areas known for coal deposits include:

1. Appalachian Mountains (Eastern United States): This region has some of the most significant coal reserves in the United States. The Appalachian coal basin extends from Pennsylvania to Alabama and contains various coal seams, including the famous Pittsburgh Coal Seam.

2. Illinois Basin (Midwestern United States): The Illinois Basin covers parts of Illinois, Indiana, and Kentucky and holds substantial coal reserves. This region is known for its high-quality bituminous coal.

3. Powder River Basin (Western United States): Located primarily in Wyoming and Montana, the Powder River Basin is home to vast coal deposits. This region is known for its low-sulfur coal, making it a popular choice for power generation.

4. Ruhr Basin (Germany): This region in western Germany is one of the most significant coal-mining areas in Europe. It has been a major source of coal since the 18th century.

5. Donets Basin (Ukraine): The Donets Basin, situated in eastern Ukraine, is another essential coal-producing region in Europe. It has been a significant contributor to Ukraine's energy supply.

6. Sydney Basin (Australia): The Sydney Basin in New South Wales, Australia, contains substantial coal reserves. This region is known for its high-quality coking coal, which is used in steel production.

It's important to note that coal deposits are not limited to these areas, as they can be found in various parts of the world where the geological conditions were favorable for the formation of coal during the Carboniferous period.