Piece of Marble Rock

If you use an Obsidian Knife on it, you will either break it or carve one of the following:

• Rough Marble Statue
• Marble Statue
• Beautiful Marble Statue

See a research article by Tibia-Stats here to discover what the chances for getting each form of the marble statues are.
See also: Piece of Marble Rock/Sculpting Statistics One can be obtained through the Jack to the Future Quest.
You can earn the achievement Marblelous by sculpting a Beautiful Marble Statue and the achievement Marble Madness by sculpting five Beautiful Marble Statues.

Before Update 8.60, this item could only be looted rarely from Eternal Guardians. With this update, however, achievements got introduced. Two of these were for sculpting Beautiful Marble Statues, which only happens one in a hundred tries. As Eternal Guardians only spawned in the area that can only be accessed once a week for the Zze Art of War task of the Children of the Revolution Quest, these achievements would be nearly impossible to get if it stayed this way. That is why Chayenne, after being made aware of this issue, added spawns of Eternal Guardians to Deeper Banuta and also added this item to the loot of Gargoyles and Stone Golems.