Lavendulan is an uncommon copper mineral, known for its characteristic intense electric blue colour. It belongs to the lavendulan group, which has four members: * Lavendulan NaCaCu5(AsO4)4Cl.5H2O * Lemanskiite NaCaCu5(AsO4)4Cl.5H2O * Sampleite NaCaCu5(PO4)4Cl.5H2O * Zdenekite NaPbCu5(AsO4)4Cl.5H2O
Lemanskiite and lavendulan are dimorphs; they have the same formula, but different structures. Lemanskiite is tetragonal, but lavendulan is monoclinic Lavendulan has the same structure as sampleite, and the two minerals form a series. analogue of zdenĕkite, and the arsenate analogue of sampleite.
Lavendulan was originally named for the lavender color of the "type" specimen, which has since been determined to be a mixture with no relationship to modern lavendulan. The mineral which is now called lavendulan is not a lavender blue color, and has no relationship to the “type” material from Annaberg. It often contains potassium as impurities.