0.18 ct METAAUTUNITE – USA

Meta-autunite

When you enter the world of secondary uranium minerals, Meta-autunite is the neon-green sentinel that demands your attention. I’ve always found it fascinating how a mineral can look so radioactive even before you bring a Geiger counter or a UV lamp near it. It forms through the dehydration of Autunite, and that transition creates a slightly different crystal structure that is actually more stable in most collector environments. But don’t let its “stable” nature fool you—it is a powerful radioactive species. Handling these specimens requires a deep respect for the material; between the intense fluorescence and the raw energy it emits, a top-tier Meta-autunite crystal is as close as most people will ever get to holding “atomic” history in their hand.

The Heritage & Discovery

Historical Significance: Meta-autunite represents a crucial chapter in the study of uranium oxidation. It is the “meta-” phase, meaning it contains less water than its parent mineral, Autunite. Historically, it has been a favorite for researchers and collectors alike because its vibrant color and intense fluorescence make it one of the most visually stunning radioactive minerals. It serves as a stark reminder of the energy stored within the earth’s crust and the complex way minerals adapt to changes in humidity and temperature.

Discovery: While Autunite has been known since the mid-19th century, the “meta” phase was specifically characterized as it became clear that most “Autunite” in collections had naturally dehydrated into this more stable form. The name stems from the type locality in Autun, France, where the original phosphate series was first identified. It has since become the benchmark for the “Meta-autunite group” of minerals.

Important Mines: Some of the most spectacular, plate-like crystals come from the Daybreak Mine in Washington, USA, which is legendary for producing world-class specimens. Other historic and high-quality material has emerged from the Cunha Baixa Mine in Portugal and the Assunção Mine. These locations are prized by collectors for producing the thick, neon-green “books” of crystals that provide the most dramatic visual impact.

Mineralogical Profile

Description: Meta-autunite is a hydrated calcium uranyl phosphate that crystallizes in the tetragonal system. It is a soft mineral, sitting at a 2 to 2.5 on the Mohs scale, and is known for its perfect micaceous cleavage, which allows it to flake into thin, brittle sheets. Its most famous property is its intense yellowish-green fluorescence under ultraviolet light. Because it is radioactive, it must be stored in a well-ventilated area, away from living spaces, and inside a protective case to prevent the inhalation of any dust or radon gas. It typically presents as square, tabular crystals with a vitreous to pearly luster.

Chemical Formula: Ca(UO₂)₂(PO₄)₂·6-8H₂O