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Minecraft resource gathering/Redstone
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You can find Redstone underground at y-level 32 or below. You must mine it with an Iron-tier or higher pickaxe or it will not drop anything. It will drop 4-8 Redstone Dust, which can be used for redstone cirucits.
Witches also drop up to six peices redstone Dust.
Redstone Dust can be used on a brewing stand with most potions to make the potion last longer.