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Light-Toned Deposits: This image reveals exposed layers in Noctis Labyrinthus which may contain signatures of iron bearing sulfates and phyllosilcate (clay) minerals. Image Credit: NASA/JPL-Caltech/University of Arizona

"Although it might seem like a fictitious nomenclature, smectite is a real substance and it’s been found on Mars. It’s a clay mineral that, like a sponge, expands and contracts as it takes on liquid water. With magnesium, iron, aluminum and silica in their content, smectites are morphed into being when silicates are exposed to non-acid water. Now Mars has yielded up two such deposits that further indicate the presence of a once wetter world."

via universetoday.com