This Specimen contains many fine crystals of the exceptionally vibrant blue mineral Azurite coupled with the bright green Malachite. It is very likely that the Malachite in this piece was originally Azurite which has been pseudomorphically replaced after being exposed to open air.
Azurite is a deep blue copper mineral produced by weathering of copper ore deposits. The mineral, a carbonate, has been known since ancient times, and was mentioned in Pliny the Elder's Natural History under the Greek name kuanos "deep blue," and the Latin name caeruleum. The intense color of azurite makes it a popular collector's stone. However, bright light, heat, and open air all tend to reduce the intensity of its color over time. Azurite is also unstable in open air with respect to malachite, and often is pseudomorphically replaced by malachite. This weathering process involves the replacement of some the carbon dioxide units with water, changing the carbonate: hydroxide ratio of azurite from 1:1 to the 1:2 ratio of malachite.