Trona
A water-bearing sodium carbonate, found in samples of the asteroid Bennu: salts left by an evaporating brine.
Key facts
- Formula
- Na3(CO3)(HCO3)·2H2O
- Family
- Carbonates, sulphates, salts and weathering products
- Crystal system
- Monoclinic
What it is
Trona is a hydrated sodium carbonate, the main ore of soda ash on Earth. It forms when salty water in a closed basin evaporates, as in dried lake beds in California and Wyoming.
Where it is found
Traces of water-bearing sodium carbonates were found in the samples brought back from Bennu by OSIRIS-REx and reported in 2025, the first time such minerals had been seen in any asteroid or meteorite. With other salts, they record an evaporating brine inside Bennu's parent body. The brine differed from Earth's soda lakes: it was rich in phosphorus and lacked boron.
How it is recognised
It forms soft, white, water-soluble crystals. In the Bennu samples it was identified by electron microscopy, spectroscopy and diffraction under conditions that protected it from Earth's air.
Did you know?
Salts like these have been seen on Saturn's moon Enceladus and are suspected on Jupiter's moon Europa.
Such fragile salts would quickly dissolve or change in a meteorite falling through Earth's atmosphere and lying on the ground.