Clarkeite
A dark-brown to reddish uranium oxide formed when uraninite oxidizes and is replaced late in pegmatite crystallization.
Intro adapted from Wikipedia (CC BY-SA).
Clarkeite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Na(UO₂)O(OH)·nH₂O.
It crystallizes in the hexagonal crystal system (space group R-3m).
Key properties: Mohs hardness 4–4.5; specific gravity 6.29–6.39; Yellowish brown streak; Slightly waxy luster; optically biaxial.
IMA symbol Cke, grandfathered status — known before the IMA’s founding, named in 1931.
Replacing uraninite, as a late-stage hydrothermal alteration product.
It is found associated with Uraninite, uranophane, wölsendorfite, fourmarierite, vandendriesscheite, becquerelite, curite, “gummite”, quartz.
The mineral was named to honor Frank Wigglesworth Clarke (1847–1931), prominent American geochemist of the U.S. Geological Survey.