The X can be either arsenic or phosphorous. Agardite actually represents at least a couple of minerals and is sometimes considered a mineral group itself. Agardite and mixite are difficult to differentiate. But if the specimen is associated with other bismuth minerals, than this can prove diagnostic in mixite's favor. Luster is vitreous or silky to dull.
Crystals are transparent to translucent.
Crystal System is hexagonal. Crystal Habits include radiating clusters, tufts or spherules of acicular or fibrous crystals, also massive, capillary and earthy. Cleavage not noticeable. Fracture is fibrous. Hardness is 3 - 4.