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mineral formations of unstable composition that comprise mixtures of cryptocrystalline aggregates consisting of hydrated oxides and some uranium hydrosilicates. The principal minerals that form gummite are clarkeite (Na, K)2 − 2r(Ca. Pb)rU2O7.y H2O, fourmarierite PbO-4UO3-7—8H20, and kasolite Pb(U02)[Si04]H20; they are rarely found in pure form. Gummite forms thin crusts and irregular or circular concretions with a conchoidal fracture and a light-yellow or red-orange resinous luster. Its hardness on the mineralogical scale is 2.5–3 and its density. 4,700–5,800 kg/m3. Gummite is brittle. It develops as a result of changes in uraninite or pitchblende in the zone of oxidation of primary uranium ores.
G. P. BARSANOV