Minecraft wiki entry for Fortune, associated text: For coal ore, diamond ore, emerald ore, lapis lazuli ore, redstone ore, iron ore, copper ore, gold ore, nether gold ore, nether quartz ore, and amethyst clusters, Fortune I gives a 33% (1⁄3) chance to multiply drops by 2 (averaging 33% (1⁄3) increase), Fortune II gives a chance to multiply drops by 2 or 3 (25% (1⁄4) chance each, averaging 75% (3⁄4) increase), and Fortune III gives a chance to multiply drops by 2, 3, or 4 (20% (1⁄5) chance each, averaging 120% (11⁄5) increase).