Any water rushing through the Martian valleys would therefore have to have vanished before the olivine was deposited.

ECONOMIST: Martian chronicles

The gems are olivine--a mineral class that includes semiprecious peridot--and can range in color from deep green to bright yellow.

FORBES: Hot Rocks

The latter process occurs at low temperatures when rocks rich in the minerals olivine and pyroxene react chemically with water, releasing methane.

BBC: Martian methane mystery deepens