It is a secondary mineral which contains lead, copper and selenium, it is a bottle green to brown/yellow color, its crystal habit varies depending on where it is found.

It has pleochroic attributes, which means depending on which axis it is seen, the gem displays different colors, which is an optical phenomenon.

[2] Demesmaekerite has a very strong radioactivity, 1,629,108.74, measured in GRapi (Gamma Ray American Petroleum Institute Units).

It is mostly made out of oxygen (22.1%), uranium (21.92%) which causes its irradiative attributes, selenium (21.81%), lead (19.08%) which is a poisonous chemical element and copper (14.63%), but also contains hydrogen (0.46%).

[4] It can be found associated with other rare selenium-bearing uranium ores, such as haynesite, guilleminite, marthozite and piretite.