Lavendulan is biaxial (−), and most sources quote values for three refractive indices, for light travelling parallel to the three crystal axes.

[6] In 1853, Vogel found a specimen of lavendulan from Jáchymov, also in the Ore Mountains, which was similar in appearance and characteristics to the material from Annaberg.

[6] In 1877 Goldsmith examined some specimens of a turquoise blue arsenate of copper from the cobalt deposits of San Juan, Chile, and announced that they were also lavendulan.

[6] Nearly fifty years later, In 1924, William Foshag announced that the Chilean material was entirely distinct from that from Jáchymov, and he determined that it was a new mineral, and gave it the name freirinite, from the locality, the Blanca Mine, Freirina, Huasca Province, Atacama Region, Chile.

[8] Yet another fifty years passed, and in 2007 Geister et al. re-examined Breithaupt's type specimen and found that it was a mixture unrelated to modern lavendulan.

[5] At the Cap Garonne Mine, Pradet, Var, Provence-Alpes-Côte d'Azur, France, associated minerals are chalcophyllite, cyanotrichite, parnauite, mansfieldite, olivenite, tennantite, covellite, chalcanthite, antlerite, brochantite and geminite.

[5] It also occurs at Tsumeb, Namibia, associated with cuprian adamite, conichalcite, o'danielite, tsumcorite, fahleite, quartz, calcite and gypsum.