Noun
Blue carbonate of copper; blue malachite.
Source: Webster's dictionaryThe search for the perfect blue During the 17th and 18th centuries, chemists in Europe tried to discover a way to create synthetic blue pigments, avoiding the expense of importing and grinding lapis lazuli, azurite and other minerals. Source: Internet
Pigments made from azurite were less expensive, but tended to turn dark and green with time. Source: Internet