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Mining nodes in
World of Warcraft will provide two to four ores before they disappear if they are normal, and up to four to eight if they are "rich" nodes.
Nodes that show red will not be able to be mined, those that are orange will always up your mining skill, yellow ones will up your mining skill 3/4 of the time, the green ones will up your mining skill half the time or less, and the grey ones will never up your mining skill.
You will often fail when mining nodes that appear as orange type, you may fail sometimes with the yellow type ones, and never fail on the green and gray type ones.