EUDIDYMITE

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

Eudidymite is a rare sodium beryllium silicate, dimorphic from epididymite. It is a mineral found in the pegmatites of nepheline syenites, associated in particular with albite, aegyrine, nepheline and eudialyte. It takes its name from the Greek eu (good) and didumos (twin) because it almost always appears in twinned crystals. Eudidymite forms centimeter-sized tabular to lamellar crystals, commonly twinned, micaceous or spherolitic aggregates with a fibroradiated texture, or fine-grained masses. Usually colorless to white, eudidymite can also be shades of purple, bluish or yellow.

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

Eudidymite in the World

Magnificent centimeter-sized eudidymite crystals were discovered in the alkaline syenite complexes of Ilimaussaq (Narssaq, Greenland), Mont St-Hilaire (Canada), and in the alkaline pegmatites of Mont Malosa (Malawi), in crystalline aggregates of 5 cm. Beautiful crystals are also known from the alkaline rocks of Lovozero (Kola, Russia) and southern Norway, in the Langesundsfjorf.

Eudidylite in France

Eudidymite is not present in the French underground.

Twinning

Twins are common on {001} forming V-shaped and star-shaped.

Fakes and treatments

No fake listed for this mineral species.


Hardness : 6
Density : 2.55
Fracture : Irregular
Streak : White

TP : Translucent to transparent
RI : 1.545 to 1.551
Birefringence : 0.006
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None

Solubility : Hydrofluoric acid


Magnetism : None
Radioactivity : None