Azurite to malachite

This is a photo from an azurite, or at least of what it is left from it. The blue mineral surviving mayhem of green invaders is our protagonist today. It is one of the two copper carbonate hydroxides, but as it can be seen on the photo, it is not the most stable.
The other one is malachite, usually produced when azurite is exposed to humidity in the air, as it slowly degrades and loses its vibrant blue colour to become greenish.

Yet even though they seem to be very different, their properties and their behaviour are very similar. In fact, both have the same crystal structure, the reason for their stability differences is that azurite is simply more carbonated. Moreover, as we know from other carbonated minerals, they are usually victims to water, which preys on carbonate unleashing carbon dioxide. That is why CuCO3 does not exist; it would be even more unstable.

However, that cannot be said with malachite. It should too be prompt to degrade even more, but it needs something more than humidity: acid. Surely, something not recommended doing if you appreciate coloured minerals.

Author: Sergi Batlle