Wiktionary
n. (context mineralogy English) An orthorhombic mineral containing arsenic, calcium, chlorine, copper, hydrogen, oxygen, and sodium.
Wikipedia
Lavendulan is an uncommon copper arsenate mineral, known for its characteristic intense electric blue colour. It belongs to the lavendulan group, which has four members:
- Lavendulan NaCaCu(AsO)4Cl.5HO
- Lemanskiite NaCaCu(AsO)4Cl.5HO
- Sampleite NaCaCu(PO)4Cl.5HO
- Zdenĕkite NaPbCu(AsO)4Cl.5HO
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. It is the calcium 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, cobalt and nickel as impurities.