The Marble, along with other Construction Materials, is sometimes needed to finish Community Buildings. These buildings do not need Staff Members. It can be gifted from friends, from FarmVille Balloon, or purchased for 2 Cash each.
There is also a random chance of acquiring this item by putting it on your wishlist and either opening a Mystery Gift or clicking a neighbor's train wall post. You also have a chance of getting this from the Daily Reward Delivery.
This item has an inventory limit of 15.