Specimen at a glance
| Mineral | Aragonite |
|---|---|
| Chemistry | CaCO3 |
| Mohs hardness | 3.5–4 |
| Crystal system | Orthorhombic |
| Locality | Rio Tinto Mine, Spain |
| You receive | The exact specimen pictured |
About this specimen
A striking blue-green aragonite specimen from the Bronces workings at the historic Rio Tinto Mine in Huelva, Spain — one of the oldest continuously worked mining districts in the world, with a documented history stretching back over five thousand years to Iberian, Phoenician, and Roman copper and silver extraction. The distinctive blue-green color seen on this piece is caused by trace copper minerals, likely malachite or related copper carbonates, coloring the aragonite as it crystallized within the mine’s copper-rich sulfide deposits. Aragonite is a polymorph of calcium carbonate, chemically identical to calcite but crystallizing in a different structure that often produces these sparkling, druzy, needle-like crystal crusts rather than calcite’s typical rhombohedral faces. Rio Tinto’s extreme mineral chemistry, including some of the most acidic natural waters on Earth, has made the district a source of unusual and vividly colored secondary minerals prized by collectors worldwide. This piece shows excellent druzy sparkle across its blue-green crystal crust set against darker matrix, making it a standout specimen for anyone collecting copper secondary minerals or classic Spanish locality pieces.
Aragonite: the science
- Aragonite and calcite are polymorphs: same formula, different atomic arrangement, and different crystal shapes.
- Pearls and mother-of-pearl are made of aragonite built by mollusks.
- Aragonite is slightly unstable at Earth’s surface and slowly converts to calcite over geologic time.
Go deeper
Want the full story on aragonite: how it forms, how to identify it, and what makes a great specimen?
Questions about this piece
What is aragonite?
Aragonite has the same chemistry as calcite, calcium carbonate, but a different crystal structure. Blue aragonite owes its color to traces of copper.
Where was it found?
This piece comes from Rio Tinto Mine, Spain. We list a locality whenever it is known, because where a mineral formed is part of its story and its value.
How hard is it, and how should I care for it?
It rates 3.5–4 on the Mohs scale. Mohs 3.5–4. Keep away from acids and harsh cleaners, and dust gently. Avoid prolonged sunlight on blue pieces.
Is this the exact piece I will receive?
Yes. This listing was photographed individually, and you receive the exact piece shown in the photos.
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