Herderite - Encyclopedia

    Class : Phosphates, arsenates, vanadates
    Subclass : Anhydrous phosphates
    Crystal system : Monoclinic
    Chemistry : CaBe(PO4)F
    Rarity : Uncommon

Herderite is a fairly rare phosphate from granitic beryl pegmatites, where it constitutes one of the last minerals to crystallize. It was discovered in small crystals (15 mm) in a tin mine in the German Erzgebirge. Some mineralogists currently tend to differentiate herderite sensu stricto, with dominant fluorine, from hydroxylherderite (with dominant OH). However, the attribution to one or the other of these minerals requires detailed analyzes which are not always possible (nor carried out on old samples). It was named in honor of Siegmund August Wolfgang von Herder, representative of Mines in Freiberg (Saxony, Germany). Herderite occurs in chunky to elongated prismatic crystals, or thick tabular with slightly rounded faces, with a pseudohexagonal appearance. It also forms botryoidal aggregates with a fibroradiated structure, or cryptocrystalline. Transparent to translucent, glassy to greasy in luster, herderite is usually colorless, yellowish white to greenish yellow and pale grayish green, sometimes brownish, rarely blue to purple (dichroism which reflects the exceptional "alexandrite effect" of certain Brazilian samples ).

Main photo : Hydroxylherderite from Xanda mine, Virgem da Lapa, Minas Gerais, Brazil © Rob Lavinsky

Twinned hydroxylherderite from Golconda, Minas Gerais, Brazil © Rob Lavinsky
Botryoidal hydroxylherderite from Emmons, Greenwood, Maine, USA © Henry Minot
Hydroxylherderite from Shigar, Gilgit-Baltistan, Pakistan © Molin Lee
Twinned hydroxylherderite from Zequinha Menezes, Minas Gerais, Brazil

Herderite in the World

Herderite is common in pegmatites in Maine (especially Greenwood), New Hampshire, and California (near Mesa Grande). However, the most beautiful groups of crystals were discovered in the pegmatites of Minas Gerais (Brazil): Galiléia (decimetric yellow-brown crystals and 7 cm twins), and especially Virgem da Lapa (prismatic crystals, sometimes bipyramid, with a purple to blue, commonly reaching 3 cm and exceptionally 17 cm, associated with tourmaline or topaz).

Herderite in France

In France, herderite is known in xenomorphic grains in the leucogranite of Echassières (Allier).


Twins on {100} or {001} with fishtail shapes are common. Most crystals are twinned ; however, some show no outward signs of this morphology.

Fakes and treatments

No fakes recorded for this mineral species.

Hardness : 5 to 5.5
Density : 3.02
Fracture : Sub-conchoidal
Streak : White

TP : Translucent to transparent
RI : 1.556 to 1.620
Birefringence : 0.033
Optical character : Biaxial -
Pleochroism : None
Fluorescence : Yellow to blue

Solubility : Acids

Magnetism : NoneRadioactivity : None


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