Dark Shard

The Dark Shard is a Hardmode crafting material used solely to craft the Dao of Pow. It has a 1/10 (10%) chance of being dropped by Dark Mummies in Corrupted or Crimson Deserts. As of the 1.3 update, it also has a 2/30 (6.67%) chance to drop from the Tainted/Vile Ghouls which respectively spawn within the Crimson/Corrupted underground desert. The equivalent for the Hallow is the Light Shard, which drops from Light Mummies and Dreamer Ghouls.

Trivia

 * The Dark Shard represents the "Yin" of "Yin Yang" or Taijitu on the Dao of Pow.