There are two way to do this. 1. **The Stockpile Way** By designating a stockpile right next to your masons workshop, and only allowing the stone you want to use on that stockpile, and removing/forbidding all other stone around the workshop, the mason will grab the stone you want him to use, as that is the closest availble stone. 2. **The Fortress Way** *(The name of this way is a reference to "Obsidian Fortress", where only obsidian is being used for the whole fortress.)* You can simply disallow usage of all other type of stone trough the <kbd>Z</kbd> -> Stone Menu.