The Site
Discover its history, geology and mineralogy
Geological Characteristics and Formation
The pyrite deposit of Navajún, located in the province of La Rioja, Spain, is one of the most renowned in the world due to the spectacular nature of its crystals and the uniqueness of its genesis, which is associated with hydrothermal metamorphism. The pyrite deposits in the area are found mainly within the materials of the Urbión Group, particularly at the contact with the Enciso Group. Mineralization occurs in layers of Cretaceous (Wealden) marls, with considerable lateral continuity that favors the abundance of pyrite outcrops. The process of hydrothermal metamorphism has mobilized sulfur from surrounding areas into the sediment, where the iron in the marls combines with the sulfur to form pyrite.
Morphology and Distribution of the Crystals
The pyrite crystals that surface in this region display a remarkable variety of forms, including cubes, pentagon-dodecahedrons, cuboctahedrons, and aggregates with a distinctive "pinecone" shape. Crystal sizes range from a few millimeters up to 20 cm in edge length, although the most notable specimens typically reach up to 10 cm. The crystals exhibit a strong metallic luster and a brass-yellow color when unoxidized. The mineralization occurs in marl layers of variable thickness, generally around 2.5 meters, with an average dip of 15°, which influences both the distribution and morphology of the pyrite crystals as well as their oxidation state.
Exploitation and Scientific and Economic Value
Within the “Ampliación a Victoria” concession, three levels of pyrite mineralization have been identified: the first, second, and third levels. The first level has been the most extensively worked, as it contains the highest quality and largest crystals. Pyrite in this level is predominantly found in cubic form, although cubo-octahedral shapes and pyritohedrons are also present. The mineralization exhibits significant spatial variability in terms of crystal size, shape, and degree of oxidation. In addition to pyrite, secondary minerals such as gypsum, chlorite, and some manganese minerals have been identified. This deposit is of great interest not only to mineralogists and geologists, but also to industry particularly for sulfuric acid production. The Navajún deposit has become a global reference point due to both the exceptional quality of its crystals and its geological and economic significance.
