Meta-Autunite

Specimen Origin: Galileia (Minas Gerais, Brazil)

The Galileia region in eastern Minas Gerais is best known for its rich pegmatites that have produced gem-quality tourmaline, beryl, and numerous rare secondary minerals. Within certain uranium-bearing pegmatite environments, alteration and weathering processes have yielded secondary phosphates, including meta-autunite. Specimens from Galileia typically occur as delicate yellow-green crystalline crusts and thin plates coating fractures and cavities in granitic rock. These are appreciated by collectors for their sharp fluorescence and their occurrence in a classic Brazilian pegmatite district.

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Meta-autunite

Meta-autunite is a hydrated calcium uranyl phosphate with the formula Ca(UO₂)₂(PO₄)₂·6–8H₂O. It usually forms as thin tabular crystals, scaly aggregates, or crusts, yellow to greenish yellow in color, with strong fluorescence under ultraviolet light. Meta-autunite represents a dehydration product of autunite, stabilizing under lower humidity conditions. It is relatively soft, strongly radioactive, and occurs in the oxidation zones of uranium deposits and pegmatites.