News!

I'm actually quite excited by this news, but I don't really know why.

NASA has been orbiting Mars for some time now looking for water or evidence of past water. Taking a lead from conditions in Central Australia, they decided that the best way to find if water once flowed on Mars was to find opal. Opal is formed when water permeates silica in a low pressure environment. As there's a lot of silica on Mars and not a lot of pressure either, NASA figured that if there had been water, there would now be opal. NASA included on the latest orbiter a spectrometer that can detect opal deposits from orbit. And now they've found some!

As opal usually forms underground they haven't found a lot, only some which appears to have been uncovered by a landslide on the side of a cliff.

Still, it's official: Opals are found on another planet. They now join diamonds (found in crater edges on the moon) and moissanite (found in comets) as the only known extraterrestrial gemstones.