Blizzard Details Diablo 3 “Runestones”
How do runestones work? Each of the 100+ skills in the game can be modified with one of five runestones, resulting in 500+ combinations.
There are five runestone types: Crimson, Indigo, Obsidian, Golden, and Alabaster. Each runestone affects skills differently. For instance, this is how the iconic Barbarian Whirlwind skill is affected:
Crimson - Shoots bits of rock and gravel in every direction, dealing area effect damage.
Indigo - Barbarian spawns smaller whirlwinds which deal direct damage.
Obsidian - Provides the barbarian with immunity to immobilizing effects.
Golden - Reduced Fury cost.
Alabaster - Critical strikes confuse enemies, forcing them to attack their allies for a short time.
The visual effect is also altered, so astute players can deduce which runestone is applied to a skill based on visual clues alone.
Visit the official page for more details and videos showcasing the visual effect changes on skills for all five classes.