Pale carbonate crystals with blue copper mineral growing across them, from a copper mine in Chihuahua.
Copper deposits are grey and dull at depth. Down there the copper sits locked in sulphides, mostly chalcopyrite, and it looks like nothing at all. The colour appears near the surface, where groundwater and oxygen have had a few million years to work on the ore and break it apart. Copper released from the sulphides recombines with whatever else is dissolved in the water, and the results are blue and green.
That zone is called the oxidation zone, and it is where nearly every beautiful copper mineral on Earth comes from. Azurite, malachite, chrysocolla, turquoise. All of them are copper ore in the process of falling apart.
Very soft, and copper minerals are toxic if swallowed. Dust with a dry brush rather than washing, keep it away from children and pets, and wash your hands after handling.
Mineral: Calcite (calcium carbonate, CaCO₃) with blue copper minerals
Crystal system: Trigonal (calcite)
Origin: Río Tinto Mine, Labor de Terrazas, Chihuahua Municipality, Chihuahua, Mexico
Hardness: Calcite is 3 on the Mohs scale and the blue coating is softer
Treatment: None
Dimensions: 10.64 x 6.5 x 17.2 cm
Weight: 0.555 kg
You will receive the exact piece photographed.