A bright yellow mineral found as an alteration product on uranium ores, typically as crusts or aggregates of slender crystals.
Uranopilite is a hydrated basic uranyl sulphate, (UO₂)₆SO₄(OH)₁₀·12H₂O. Crystal system: monoclinic.
Late 19th century; earliest use found in American Journal of Science. From urano- + ancient Greek πῖλος wool, felt + -ite, after German Uranopilit, so called on account of its appearance.