Nasa's Curiosity rover finds 'unusual rock'

It was expected to be just another lump of dull basalt, but the first rock examined up close by Nasa's Mars rover proved to be a little more interesting.

The pyramidal object, nicknamed "Jake Matijevic" after a recently deceased mission engineer, had a composition not seen on the planet before.

Scientists have likened it to some unusual but well known rocks on Earth.

These form from relatively water-rich magmas that have cooled slowly at raised pressures, said Edward Stolper.

"[The rock is] widespread on Earth, on oceanic islands such as Hawaii, and St Helena, and the Azores; and also in rift zones like the Rio Grande and so forth. So, again, it's not common, but it's very well known," the mission co-investigator from the California Institute of Technology, Pasadena, told reporters.

The Curiosity rover examined Jake Matijevic three weeks ago. At the time, the dark rock was not anticipated to have high science value; it was merely an early opportunity to use the robot's survey instruments in unison.

Jake Matijevic also had an interesting, weathered appearance that drew attention.

The rover first zapped the rock from a distance with its ChemCam laser, and then moved in close to study it with its X-ray spectrometer known as APXS. The latter device is held on the end of the rover's robotic arm; the laser is mounted on its mast.

Jake Matijevic was found to be high in elements consistent with the mineral feldspar, such as sodium and potassium, and low in elements such as magnesium and iron.

Prof Stolper compared the signatures with a catalogue containing thousands of Earth rocks, and determined the nearest match to be an igneous type, the formation of which he likened to the production of colonial apple jack liquor.