PICROPHARMACOLITE

    Class : Sulfates, chromates, molybdates
    Subclass : Hydrated arsenates
    Crystal system : Triclinic
    Chemistry : Ca4Mg(AsO4)2(HAsO4)2 11H2O
    Rarity : Uncommon

Picropharmacolite is the most common calc-magnesium arsenate. It is formed by oxidation of primary arsenic minerals, mainly native arsenic and löllingite, but also realgar, in the upper part of the deposits. Its name comes from the Greek pikros (bitter) and pharmakon (remedy, poison), in reference to the taste of the mineral and its arsenic content. Picropharmacolite is common in newly formed efflorescence in old mining works where it composes aigrettes and spherules or sea urchins of white acicular crystals (sometimes pink when it presents traces of cobalt) up to 2 cm, frequently associated with pharmacolite. It is a highly hydrated mineral that easily loses its water in a dry atmosphere.

Main photo : Picropharmacolite from Giftgrube mine, Ste-Marie-aux-Mines, Haut-Rhin, France © William Peraud

Picropharmacolite from Salsigne, Aude, France
Pink picropharmacolite from Wilhelm Mine, Hesse, Germany © Nadya Georgieva
Picropharmacolite from Anton Mine, Wittichen, Germany © Uwe Haubenreisser
Picropharmacolite on realgar from Matra, Haute-Corse, France © Sylvano Iob

Picropharmacolite in the World

Picropharmacolite is known in the United States at the Getchell mine (Nevada) which produced centimeter-sized crystals. The German mines of the Erzgebirge (Freiberg, Mareinberg, Annaberg...) are rich in efflorescences and more rarely in small crystals of picropharmacolite. The Forët Noire deposits provided samples of better quality, close to the French specimens. Generally speaking, we can expect to find picropharmacolite at the apex of arsenic mineralization in the context of basic rocks (rich in calcium and magnesium).

Picropharmacolite in France

In France, picropharmacolite is classically found in the mining district of Ste-Marie-aux-Mines (Haut-Rhin), where it forms splendid sea urchins measuring 2 to 3 cm, made up of needles measuring 1 to 2 cm. It is found there associated with numerous other calc-magnesian arsenates. These samples are among the most beautiful in the world. Beautiful hilly groups are also known in Salsigne (Aude), it is also reported in Duranus and Lucéram (Alpes-Maritimes) as well as in Matra (Haute-Corse).

Twinning

No twins known for this mineral species.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 1 to 2
Density : 2.55 to 2.64
Fracture : Fibrous to micaceous
Streak : White

TP : Translucent
RI : 1.556 to 1.585
Birefringence : 0.021
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None

Solubility : -

Magnetism : NoneRadioactivity : None

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