Gypsum
A calcium sulphate found in white veins in CI chondrites, partly grown after they reached Earth.
Key facts
- Formula
- CaSO4·2H2O
- Family
- Carbonates, sulphates, salts and weathering products
- Crystal system
- Monoclinic
What it is
Gypsum is a soft, water-bearing sulphate of calcium. It forms when water rich in sulphate evaporates or reacts with calcium-bearing rock.
Where it is found
White veins of gypsum and other sulphates cross the Orgueil CI chondrite. Their origin has been debated: some formed on the parent body, but studies show that much of the sulphate grew after the fall, as sulphides reacted with Earth's moist air. Samples from Ryugu, kept away from air, contain very little sulphate, supporting that view. Gypsum also forms in weathered desert finds.
How it is recognised
It is white, very soft, and can be scratched with a fingernail.
Did you know?
The absence of sulphate veins in Ryugu grains showed that some features of CI meteorites were caused by their time on Earth.
Gypsum has also been found in veins on Mars by the Opportunity and Curiosity rovers.