Marble Cobblestone is a slightly brighter version of the regular Cobblestone. It is as durable, but is slightly less useful than Cobblestone since it's not possible to craft tools or weapons with Marble Cobblestone. Similarly to Marble, it is softer (quicker to mine) than cobblestone.
Marble Cobblestone is only used as a building material and can be smelted in the oven to get Marble Stone, like regular Cobblestone.
It can be crafted into various types of bricks, stairs, pavers and more.