Certain marble is a type of marble that is made up of three different types of marbles. The first type is Steelie, which is a type of marble made of steel and is seven letters long. The second type is Catseye, which is a type of marble made of glass and is also seven letters long. The third type is SHOOTER, which is a type of marble made of clay and is also seven letters long. All three types of marbles are used to create Certain Marble.