PUMPELLYITE

    Class : Silicates
    Subclass : Sorosilicates
    Crystal system : Monoclinic
    Chemistry : Ca2MgAl2(SiO4)(Si2O7)(OH)2 H2O
    Rarity : Fairly common to common

Pumpellyite is a group of silicates close to epidote, subdivided into four minerals according to the predominant element or ion : Mn, Fe2+, Fe3+ and Mg, the latter being by far the most abundant. Pumpellyite is widely distributed in rocks of very different compositions and geological contexts, with a predilection for slightly metamorphic rocks, which has made it a valuable indicator for measuring early metamorphism (the prehnite-pumpellyite facies). In all cases, it would be of hydrothermal origin, in connection with the fluids released during metamorphic events. It was named in honor of Raphael Pumpelly, who was the first to study the paragenesis of copper minerals from the Keweenaw Peninsula (Michigan) deposit. Pumpellyite is a fibrous mineral, sometimes lamellar, commonly giving acicular star-shaped aggregates, or tufted feltings. Its color is variable, usually pale grayish-green, dark green to black-green, dark brown, sometimes bluish green. The chatoyant chlorastrolite variety is polished and sometimes used in jewelry or as an ornamental stone.

Main photo : Pumpellyite from Pastina quarries, Tuscany, Italy © Bruno Marello

Pumpellyite from Costa Sopramare, Liguria, Italy © Gianfranco Ciccolini
Pumpellyite from Los Arenales, Spain © Paul Mestrom
Pumpellyite from Creag Brimishgan, Scotland, UK © Henk Smeets
Pumpellyite (chlorastrolite variety) from Phoenix Mine, Michigan, USA © Matt Heilman

Pumpellyite in the World

Among the many deposits where this mineral is present, we must mention the crystals discovered in the cavities of the copper basalts of Calumet (Michigan) for their very particular context. Pumpellyite is also common in good specimens in the glaucophane and lawsonite schists of several California localities in Sonoma County and in the Honshû metamorphic belts (Japan). It was also encountered in the more surprising context of the hydrothermal gold deposit of Hemlo (Ontario, Canada). Very beautiful crystals have also been reported from Groppaggi (Italy).

Pumpellyite in France

In France, pumpellyite is reported in the alluvial deposits of the Durance (Bouches-du-Rhône).

Twinning

Twins are common on {100} and {001}.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 5.5
Density : 3.18
Fracture : Undetermined
Streak : White

TP : Opaque to translucent
RI : 1.674 to 1.764
Birefringence : 0.014 to 0.016
Optical character : Biaxial +
Pleochroism : Strong
Fluorescence : None

Solubility : Insoluble

Magnetism : NoneRadioactivity : None

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