Azurite is an opaque pale blue to deep blue mineral variety of copper carbonate. Often found with malachite, azurite has been referred to as blue malachite.
Giving Depth to the Seas
Michelangelo used azurite as a less expensive alternative to lapis lazuli for making blue pigment. As a result of being a major ore of copper, as is turquoise, azurite tends toward greener shades of blue. Lapis lazuli, which makes the pigment called ultramarine, tends toward more violet shades of blue. Michelangelo said that while ultramarine gave height to the skies, azurite gave depth to the seas. Azurite is still used as a blue dye for paint and fabric.