The Thief Stone (Skyrim)

Description
The Thief Stone is one of the first three Guardian Stones the player can choose from. The stone improves stealth associated skills 20% faster.

The Thief skills are:
 * Alchemy
 * Light Armor
 * Lockpicking
 * Pickpocket
 * Sneak
 * Speech

Location
After finishing the introductory mission, continue to follow the NPC (Ralof-Rebellion or Hadvar-Imperial ) and they will lead you to it. It is located southwest of Riverwood, and north-northwest of Helgen. The map marker is a pillar with a black diamond. Choosing this stone is great for a stealth based character such as an assassin.

The Mage Stone and The Warrior Stone can be found at the same place.