2.91 ct CORONADITE – MOROCCO

strong>Coronadite

Coronadite is a gemstone that represents the “hidden” metallic elegance of the manganese oxide group. A lead manganese oxide, it is a mineral I have always respected for its dense, heavy presence and its sophisticated, “gunmetal” aesthetic. It typically forms as dark grey to iron-black botryoidal (grape-like) crusts or as compact, fibrous masses that possess a sub-metallic to dull luster. For the specialist, Coronadite is a stone of the oxidation zone, representing the chemical meeting point between lead and manganese in arid environments. It is a prize of structural density—while it may appear humble at a glance, its high specific gravity and “velvety” black surfaces make it a standout for those who appreciate the dark, grounding minerals of the deep veins.

The Heritage & Discovery

Historical Significance: Coronadite is a vital species for understanding the mobility of lead within manganese-rich “gossans” or iron caps. Historically, it was a significant discovery because it provided a clear example of the hollandite supergroup structure, where large cations like lead are trapped within a framework of manganese oxide “tunnels.” In the world of fine minerals, it is celebrated for its rare, high-gloss botryoidal forms that can look like polished hematite but with a distinct, “heavy” chemical signature. It stands as a symbol of the rugged endurance of the desert, bridging the gap between raw manganese ores and the elite world of rare, dark-colored collector minerals.

Discovery: The mineral was first described in 1904 and was named in honor of the Spanish explorer Francisco Vásquez de Coronado (1510–1554), who led a major expedition through the American Southwest where the mineral was first identified. The type-locality is the Coronado Vein in the Clifton-Morenci District of Arizona, USA. Naming this dense, “metallic” mineral after an explorer of the rugged frontier was a fitting tribute to the geological exploration of the New World. Since its formal identification, it has become a staple for those collecting the complex oxides of the great copper and lead belts.

Important Mines: The legendary and type-locality for world-class Coronadite is the Morenci Mine in Arizona, USA. I also have a high regard for the spectacular, high-gloss specimens found in the Imini Mine in Morocco and the thick, fibrous crusts from the Broken Hill region in Australia. For the vault, I prioritize the Moroccan material for its exceptional “wet-look” luster and the Arizonan pieces for their unmatched historical pedigree and association with other rare secondary minerals.

Mineralogical Profile

Description: Coronadite is a lead manganese oxide that crystallizes in the monoclinic system (though it often appears massive or fibrous). It sits at a 4.5 to 5 on the Mohs scale, making it a relatively durable mineral that takes a fine, metallic polish. It is characterized by its sub-metallic luster and its deep iron-black to dark grey color.

One of its most identifying traits is its high density ($SG \approx 5.4$ to $5.5$), which gives even small pieces a surprising “heaviness” in the hand. It has a brownish-black streak, which helps distinguish it from other black oxides like Romanechite. Because it belongs to the hollandite group, its structure is characterized by “tunnels” that can host various large ions. When I select a piece for the collection, I look for “fresh,” unbroken botryoidal surfaces with a high-reflectivity luster, as these represent the species in its most perfect and aesthetic form. It is a dense, grounding mineral that offers a unique, “industrial” beauty unlike any other manganese species.

Chemical Formula: Pb(Mn⁴⁺₆Mn³⁺₂)O₁₆