New York Times
: Since landing on Mars in 2012, NASA’s Curiosity
rover has been exploring Gale Crater, a 154-km-wide depression on the planet’s surface. Among its many discoveries is its most recent finding that some of the sedimentary rock in the crater contains significantly more silica than usually seen in basaltic rock. After detailed examination, the phase of silica turned out to be tridymite, which is rare on Earth and had never been seen on Mars. How sedimentary rocks ended up with so much silica, which on Earth usually forms in volcanic or metamorphic rocks, is not yet known. Scientists say that liquid water must have been involved and that it either washed away the other elements or washed in the silica.