Autunite & Uranophane - Ruggles Mine, Grafton, Grafton County, New Hampshire, USA

Ca(UO₂)₂(PO₄)₂ · 10-12H₂O          Ca(UO₂)₂(SiO₃OH)₂ · 5H₂O

Autunite and Uranophane from the Ruggles Mine in Grafton, New Hampshire, are noteworthy examples of secondary uranium minerals. These minerals form as alteration products of primary uranium minerals like uraninite, often appearing in pegmatitic and hydrothermal environments. Their striking visual characteristics, combined with their geological significance, make them prized specimens among collectors and researchers alike.

Autunite ($Ca(UO_2)_2(PO_4)_2 \cdot 10-12H_2O$) is known for its vibrant yellow-green color and tabular crystals that exhibit a pearly luster. At the Ruggles Mine, autunite often occurs as coatings or aggregates along fractures and cavities in the host rock. The formation of autunite is driven by the interaction of uranium-bearing fluids with phosphate-rich minerals in the granite pegmatites that characterize the area. This mineral is slightly fluorescent under UV light, further enhancing its appeal to collectors.

Uranophane ($Ca(UO_2)_2(SiO_3OH)_2 \cdot 5H_2O$) is another secondary uranium mineral found at the Ruggles Mine, recognized for its fibrous to radiating crystal habit and yellow to orange coloration. Uranophane forms in similar conditions to autunite but involves the incorporation of silica rather than phosphate. Its silky texture and delicate structures often occur as crusts or radiating clusters within the pegmatite, especially in areas with extensive weathering of primary uranium minerals.

The Ruggles Mine, a historic site known for its large feldspar pegmatites, provides an ideal geological environment for the formation of these secondary uranium minerals. The interaction of groundwater with the uranium-rich deposits has facilitated the alteration of primary uranium minerals into autunite and uranophane. The mine’s mineralogical diversity, including its rich suite of uranium minerals, has drawn attention from geologists and mineral enthusiasts for decades.

Both autunite and uranophane from the Ruggles Mine are significant for their scientific value and visual appeal. They provide insights into the mobility and deposition of uranium in pegmatitic systems and the geochemical processes that govern the formation of secondary uranium minerals. While handling these specimens requires precautions due to their radioactive nature, their bright colors and unique crystal forms continue to captivate collectors and contribute to the understanding of uranium mineralogy.