Gravel ores (Iron, Gold, Copper, Tin, Aluminum, Cobalt) can be smelted in a Furnace for a single ingot, or in a Smeltery and then cast to create two ingots. Gravel ores require a Shovel to mine. Gravel ores require a certain level of shovel (i.e. a stone shovel cannot pick up gold gravel ore). Breaking a gravel ore block does not drop a block of pure gravel. Gravel ores will never drop flint.
Also, just like regular gravel, it breaks when it falls on a torch or some other irregular block. This allow you to get the resource without the need for a shovel.