Guilleminite shows strong pleochroic attributes. Depending on the axis the gem is seen, guilleminite on the X axis can be seen in a bright yellow color, on the Y axis can be seen yellow, and on the Z axis is seen as a colorless gem.

Derriksite is a very rare uranium mineral. It is a secondary mineral that contains copper, uranium and the rarer selenium. It is a bright green to duller bottle green colour. Its crystal habit is acicular, it is most likely to be found along with the uranyl selenium mineral demesmaekerite, but derriksite is much rarer than demesmaekerite.

Guilleminite is the yellow, with dark green derriksite on matrix. As a this is a uranium bearing mineral, it is radioactive.