Jarosite
A potassium iron sulphate that marks acidic water on Mars, found in a Martian meteorite and by a rover.
Key facts
- Formula
- KFe3(SO4)2(OH)6
- Family
- Carbonates, sulphates, salts and weathering products
- Crystal system
- Trigonal
What it is
Jarosite is a yellow iron sulphate with potassium and hydroxyl. It forms only in acidic water, so it is a useful indicator of past conditions.
Where it is found
The Opportunity rover found jarosite in the layered rocks of Meridiani Planum in 2004, showing that acidic water once soaked them. It has also been found in tiny amounts in the nakhlite Miller Range 03346. Because it contains potassium, Martian jarosite in meteorites has been dated by the argon method, giving an age for water activity on Mars.
How it is recognised
It is yellow to brown and identified by spectroscopy or X-ray diffraction.
Did you know?
Jarosite on Mars was among the clearest early evidence that liquid water once existed at the surface.
On Earth it forms where sulphide ores weather, such as Spain's Río Tinto.