Formula: Pb₂Cu₅(UO₂)₂(SeO₃)₆(OH)₆ · 2H₂O

Species: Oxides – (Selenites)

Colour: Bottle-green when fresh, turning somewhat brownish on dehydration

Hardness: 3 – 4

Specific Gravity: 5.28

Crystal System: Triclinic

Name: Named in 1965 by Fabian Cesbron, B. Bachet, and Robert Oosterbosch in honor of Gaston Demesmaeker [1911-1997], Belgian geologist, former director of the Union Minière du Haut Katanga (UMHK).

Type Locality: Musonoi Mine, Kolwezi, Lualaba, DR Congo.