Agates
Also known as "aggies," these marbles were actually made from a type of quartz called agate, which means they have layers of bright colors. Agates are often used as shooters and come in a variety of sizes. Marbles from early in the 20th century got their color and design from the actual elements in the marbles. Later models were often dyed to enhance their color.
Steelies
As the name implies, steelies are often made of steel, though any metal ball may be called a steelie. Rather than true marbles, steelies are actually ball bearings that are used in games often as shooters. Steelies are not allowed in official American marble tournaments.
Cat's Eyes
Cat's eyes were agates that resembled a cat's eye, with an oblong shape in the center. They are often clear glass, with a colorful central cat's eye element inside. Other cat's eyes are solid and opaque, but with the similar cat's eye design on the surface.
Boulders
Also known as "smashers," these are marbles that are larger than the commonly seen marbles and are only allowed in certain marble games. They are not used as shooters. However, boulders can be a little easier for smaller boys to handle than smaller marbles that can easily slip from little fingers.
Swirls
Swirls are handmade glass marbles made in Germany from the 1890s to the 1930s. As you might imagine, swirls earned their name from the colorful swirls that wrapped around the marbles.