Herderite

Very rare minaral of the phosphate, arsenate and vandate class.
Fluor-dominant herderite forms an isomorphous series with hydroxy-dominant hydroxylherderite.

Herderite shop

Origin of name: Firstly described by Viennese Mineralogist Wilhelm Karl Ritter von Haidinger who, upon visiting the mineralogical museum of Freiberg, Saxony, in 1823, noticed a specimen labelled "apatit" which he realized not to be apatite but a then unknown mineral. He published the description first in English (HAIDINGER, W. (1828): On Herderite, a new Mineral Species.- Philosophical Magazine, or Annals of Chemistry, Mathematics, Astronomy, Natural History, and General Science 4, 1-3), then in German and called the new mineral herderite in honour of Sigismund Freiherr von Herder, German geologist and mineralogist.

Synonyms and trade names: allogonite, fluor-herderit

Can be confused with: a number of other light green minerals like apatite, hiddenite, tourmaline, peridot etc.

Localities: type-locality is the Sauberg mountain tin mine in Saxony, Germany
Mindat.org lists several hundred localities but does not differentiate between (fluor-dominant) herderite and hydroxyl-herderite.
True fluor-herderite has only been confirmed from Brazil, Myanmar, China (Yichun), Namibia, Austria and probably Pakistan, Russia and the USA. (Wikipedia)

Two herderites from Brazil

Handling: due to the low hardness, the brittleness and the sensitivity to acid herderite is not suitable for jewellery wear. However, connoisseurs and collectors, apart from museums the only buyers of such rare gems, would never wear herderite or any other of their treasured rarities as jewellery, for fear of damaging or even losing it.

Worth knowing: Haidinger (see "origin of name") and German mineralogist Johann Breithaupt for 15 years fiercely fought over the question of who had discovered herderite first and thus had also earned the right to name it. Apparently Breithaupt, who had called the new mineral allogonite, lost and Haidinger is now acknowledged as the discoverer of herderite.

Herderite shop