Azurite sea horse
We often return to the copper carbonate minerals such as azurite and malachite, since they form in such a wide diversity of habits and display such lovely and intense blues and greens. Sometimes nature turns up evocativepatterns of crystallisation such as the naturally formed sea horse shape of this crystal group, mined in the Sonora district of Mexico last November and measuring 17.4 x 8.5 x 3.0 cm. This crystal group is what is known as a floater, found freely floating in a pocket (usually filled with clays) rather than directly connected to the surrounding rock.
Copper deposits are often (but by no means always) formed from the juices spat out by freshly emplaced cooling granites that have concentrated within them all the elements that do not fit into the crystal structures of the common granitic minerals such as quartz, feldspar and mica. The granites are effectively acting as giant Earth stills, distilling metals out of the lower crust and mantle within their magma. Once the fluids have deposited their precious cargo in veins and small fractures within the infiltrated rocks, the results are often chemically altered by contact with mineralised groundwater, which oxidises the original minerals and transforms them into secondary minerals such as copper carbonate.
Image credit: Joe Budd/Rob Lavinsky/iRocks.com