Guilleminite (Ba(UO2)3(SeO3)2(OH)4·3H2O) is a uranium mineral named by R. Pierrot, J. Toussaint, and T. Verbeek in 1965 in honor of Jean Claude Guillemin (1923–1994), a chemist and mineralogist.

It is a rare uranium/selenium mineral found at the Musonoi Mine in the Katanga Province of the Democratic Republic of the Congo.

[3] This secondary mineral also includes barium in its structure, in addition to selenium and uranium.

It is bright yellow in colour and usually has an acicular crystal habit.

[5] Guilleminite shows strong pleochroic attributes.