EPIDIDYMITE

    Class : Silicates
    Subclass : Inosilicates
    Crystal system : Orthorhombic
    Chemistry : NaBeSi3O7(OH)
    Rarity : Rare

Epididymite is a rare sodium beryllium silicate, dimorphic from eudidymite. It is a mineral found in pegmatites of nepheline syenites, associated in particular with albite, aegyrine, nepheline and eudialyte. It takes its name from the Greek epi (near) and didumos (twin) due to the existence of its dimorph. Epididymite forms centimeter-sized tabular pseudo-hexagonal crystals, micaceous or spherolitic aggregates with a fibroradiated texture, or porcelanose masses. Usually colorless to white, epididymite can also be shades of purple, bluish or yellow when it is finely crystallized.

Main photo : Epididymite of Poudrette Quarry, Mont St-Hilaire, Quebec, Canada © Martin Slama

Epididymite from Mount Malosa, Malawi © John Sobolewski
Epididymite, albite and aegyrine from Poudrette Quarry, Mont St-Hilaire, Canada © Nadya Georgieva
Epididymite and hematite from Vezná pegmatite, Czech Republic © Martin Slama
Twinned epididymite from Poudrette Quarry, Mont St-Hilaire, Canada © Matteo Chinellato

Epididymite in the World

Superb epididymite crystals come from the alkaline pegmatites of Mount Malosa in Malawi and can measure up to 7 cm, they are the largest known. Magnificent centimeter-sized crystals have also been discovered in the alkaline syenite complexes of Ilimaussaq (Narssaq, Greenland) and Mont St-Hilaire (Canada). Very good crystals are also known from these same rocks at Lovozero and Khibiny (Kola, Russia), and in southern Norway in the Langesundsfjord.

Epididylite in France

Epididymite is not present in the French underground.

Twinning

Twins are known in reticulated crystals and pseudo-hexagonal trills.

Fakes and treatments

No fake listed for this mineral species.


Hardness : 5.5
Density : 2.54
Fracture : Irregular to conchoidal
Streak : White

TP : Translucent to transparent
RI : 1.544 to 1.546
Birefringence : 0.002
Optical character : Biaxial +
Pleochroism : None
Fluorescence : Sometimes green

Solubility : Hydrofluoric acid


Magnetism : None
Radioactivity : None

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