What is Lavendulan?
Lavendulan is a rare blue to violet hydrated copper arsenate chloride, prized for colourful crusts from classic oxidised copper localities.
Mineralogy and crystal structure
Reference formula: NaCaCu5(AsO4)4Cl·5H2O. Lavendulan is a triclinic hydrated copper arsenate chloride and belongs to a group of closely related blue secondary minerals. Intergrowths and compositional variation are common, so locality and associated minerals are essential parts of a responsible label. Lavendulan is classified with arsenates and has a triclinic crystal system. Typical hardness is 2.5–3 on the Mohs scale and specific gravity is approximately 3.5–3.7.
Colour, lustre and habit
Typical colours include blue, blue-green, green, violet. The usual crusty, botryoidal, fibrous habit and vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Lavendulan forms in or is associated with supergene oxidation zones of arsenic-rich copper deposits. Important documented localities include Lavrion in Greece, Chile, Mexico, Germany and the United States.
Lavender-blue colour from a rare copper assemblage
Lavendulan is prized for a colour palette that moves from sky blue to violet and green. Its delicate crusts are especially attractive when they preserve the oxidised vein rather than being separated from the geological setting that created them.
Collecting and care
Arsenate-bearing and soft: keep enclosed, avoid dust, acids, water and any cutting or grinding, and wash hands after handling.
