Azurite

Botryoidal Azurite

Azurite is deep blue in colour (sometime so dark it can even appear black) and is a minor ore of copper.

Blue Azurite and Green Malachite

The striking difference in colour between the vivid greens of malachite and the deep blues of azurite make it difficult to believe that these two minerals are so closely related. To explore this phenomena, we need to dive back into the science.

Just like malachite, azurite is a hydrous copper carbonate that has precipitated in fractures and cavities in the vicinity of a copper deposit. Both are more valuable for their colour than for being copper ores. Malachite and azurite can have similar habits (botryoidal, stalactite, massive) and they are naturally found together.

So, how can two minerals so closely related have such different colours?

It actually boils all the way down to the molecular structure of each of them!

Specifically, azurite has one more copper ion and one more carbonate ion than malachite. That’s how closely related these two copper minerals are!

Another interesting fact… Under the right conditions, malachite can actually replace azurite creating a pseudomorph of the original azurite. A pseudomorph is a mineral formed by the chemical or structural change of another substance, but generally retains the original external shape (ie the malachite would retain the general shape of the original azurite crystals). Malachite can replace azurite, but the opposite is rarely seen because the molecular structure of azurite is less stable than that of malachite.

Tabular and Botryoidal Azurite

Tabular and prismatic crystals are also common in azurite, but not seen in malachite.

We’ve covered the science. Now, how is azurite used?

Similar to malachite, azurite has been used as a pigment for thousands of years. However, some old paintings that used azurite paints have obtained a greener hue. These paintings were likely stored in humid environments which allowed the azurite pigments to slowly weather into malachite. Today, a fixative is added to paints that contain azurite to avoid this colour change.

Like malachite, azurite is an attractive rare mineral. So, you would think that it would be as expensive and sought after as malachite, right?

Azurmalachite beads

Despite it’s attraction, pure azurite is not commonly used in jewelry because of how soft it is, it’s inclination to fracture and it’s tendency to turn green. You can find blue azurite in some simple jewelry, but it has likely been coated with a clear sealant to protect it. Lapis lazuli, which has similar colours to azurite but is much easier to work with, is used more frequently in jewelry than pure azurite.

Azurmalachite or Azurite-Malachite (a mix of blue azurite and green malachite) is much more stable than pure azurite and is readily seen in cabochons, beads and small structures. These may also be sealed to protect the blue colours.

Deep blue… greens of every shade... what colour will the next copper ore be?!?! Why turquoise, of course.