Guardian Stone

A chunk of blue, magical stone. Used in a number of recipes, generally defensive.

Source
Guardian Stone drops off Stone Guardians along the river in Un'Goro Crater.

Guardian Stone as an Ingredient
Guardian Stone is used in the following recipes:

Blacksmithing

 * Blackguard
 * Hammer of the Titans
 * Obsidian Mail Tunic

Leatherworking

 * Dawn Treaders
 * Golden Mantle of the Dawn

Tailoring

 * Argent Boots
 * Argent Shoulders
 * Cloak of Warding