Novacekite in Calcite

From the Irenee du Pont mineralogical collection.

Origin: Santa Eulalia (Chihuahua, Mexico)

The Santa Eulalia district in Chihuahua is one of Mexico’s most important and historic mining areas, producing a wide variety of lead, zinc, silver, and uranium minerals. Within oxidized zones and secondary environments, nováčekite has been documented as bright yellow coatings and crusts intergrown with or perched upon calcite crystals. The contrast of vivid nováčekite against white to clear calcite makes such specimens especially attractive and notable among collectors.

The Irénée du Pont mineralogical collection was assembled in the early 20th century by Irénée du Pont, a member of the prominent American industrial family. It became renowned for its breadth and quality, featuring fine specimens of classic minerals sourced from important localities around the world. Today, the collection is regarded as historically significant for its representation of early private mineral collecting in the United States.

Nováčekite in Calcite

Nováčekite is a hydrated magnesium uranyl arsenate with the formula Mg(UO₂)₂(AsO₄)₂·10–12H₂O. It belongs to the autunite group and typically forms lemon- to straw-yellow tabular crystals, scaly coatings, or crusts. The mineral is strongly radioactive, often fluoresces greenish-yellow under ultraviolet light, and develops as a secondary phase in oxidized uranium-rich deposits. Its occurrence with calcite provides both aesthetic contrast and mineralogical interest.