Magnesite
Magnesium carbonate, formed by water in CI chondrites, Ryugu and the Martian meteorite ALH 84001.
Key facts
- Formula
- MgCO3
- Family
- Carbonates, sulphates, salts and weathering products
- Crystal system
- Trigonal
What it is
Magnesite is magnesium carbonate. It forms a series with siderite, iron carbonate, and is related to calcite and dolomite. Carbonates in meteorites are a record of liquid water that once flowed through the parent body.
Where it is found
It occurs in CI chondrites and in samples from Ryugu and Bennu, often mixed with iron as breunnerite. The Martian meteorite ALH 84001 contains famous zoned carbonate globules that range from magnesite to siderite and calcite; they formed about 3.9 billion years ago from water on Mars.
How it is recognised
It is identified by its composition and by the way it fizzes only weakly in cold acid. Isotopes of carbon and oxygen in it show the temperature of the water.
Did you know?
The carbonate globules in ALH 84001 were at the centre of the 1996 claim of fossil life in a Martian meteorite.
Bennu's surface has bright carbonate veins visible from orbit.