TRONA

    Class : Carbonates, nitrates, borates
    Subclass : Hydrated carbonates
    Crystal system : Monoclinic
    Chemistry : Na3CO3(HCO3)2H2O
    Rarity : Common

Trona is a common evaporite mineral. It results mainly from the evaporation of salt lakes, but also appears in efflorescence on the ground of arid regions. It is frequently associated with other evaporite carbonates and sulfates such as mirabilite, natron, thermonatrite or glauberite. Its name derives from the Arabic natron which designates the efflorescent salt of dried lakes. Trona most often occurs in fibrous or columnar masses, very rarely in well-formed crystals, then elongated according to [010] and flattened on {001}. Colorless, gray or even yellowish white, trona has a vitreous luster and an alkaline flavor. Highly soluble in water, it does not deteriorate when exposed to dry air. It is a sodium ore and in ancient Egypt it was also used for construction.

Main photo : Trona from Wadi El-Natrun, Egypt © Jason Evans

Trögerite from Weisser Hirsch Mine, Neustädtl, Germany © Uwe Haubenreisser
Trögerite from Weisser Hirsch Mine, Neustädtl, Germany © Stephan Wolfsried
Trögerite from Jachymov, Czech Republic © Alex Earl
Trögerite from Riviéral, Hérault, France © Frédéric Bonnet

Trona in the World

Trona is known from many evaporite deposits. Lake Magadi (Kenya) has provided beautiful centimeter-sized fibrous crystals. It is also present in the sodic lakes of the Western USA (Boron, Searles, Owens, etc...) associated with other salts (borax, hanksite, thenardite). It is currently formed by evaporation of alkaline brines on the shores of Lake Texcoco (Mexico), and especially Lake Chad in Kanem, where it forms spectacular crystalline plates composed of acicular crystals grouped in rosettes and sheaves. Finally, let us mention its oldest locality : near Memphis in the Nile Valley in Egypt.

Trona in France

Trona is not known in the French underground.

Twinning

No twin known for this mineral species. Trona pseudomorphs after halite cubes are known.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 2,5 to 3
Density : 2,11
Fracture : Irregular to conchoidal
Streak : White

TP : Translucent
RI : 1.412 to 1.543
Birefringence : 0.128
Optical character : Biaxial -
Pleochroism : None
Fluorescence : Possible

Solubility : Acids, water

Magnetism : NoneRadioactivity : None

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