Pumpellyite - Encyclopedia
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 in the World
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