Carbonate crystals carrying blue copper mineral, out of the Bronces workings at the Río Tinto Mine.
The deposit is a copper skarn, which is what forms when hot fluids from an intruding body of magma hit limestone and rebuild it into something else entirely. The Bronces workings cut the oxidised part of that skarn, the upper zone where the original ore has weathered, and that is where the coloured secondary minerals sit. The same ground has produced chrysocolla, malachite, azurite, hemimorphite, austinite and strashimirite.
It is not a specimen mine. It is a working copper operation, and pieces like this come out because miners coming off shift recognise something worth carrying up rather than crushing.
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: 10.23 x 6 x 14.1 cm
Weight: 320 g
You will receive the exact piece photographed.