When scientists selected a rock to test the Mars rover Curiosity's laser, they expected it to contain the same minerals as rocks found elsewhere on the red planet, but learned instead it was more similar to a rock found on earth.
The rock was chemically more akin to a type of rock found on oceanic islands like Hawaii and St Helena, as well as in continental rift zones like the Rio Grande, which extends from Colorado to Chihuahua, Mexico.
"It was a bit of a surprise, what we found," Curiosity scientist Ralf Gellert of the University of Guelph in Ontario, Canada, said on Thursday. "It's igneous," he said - rock formed from molten material. "But it seems to be a new kind of rock type that we encountered on Mars."
Curiosity arrived on Mars two months ago to learn if the most earth-like planet in the solar system was suited to microbial life.
Last month, Curiosity's laser was used to zap the football-sized rock and the rover analysed the pulverised material to determine its chemical composition.
Scientists found the rock lacks magnesium and iron - elements found in igneous rock examined by previous Mars rovers Spirit and Opportunity. It is also rich in feldspar-like minerals, which gave clues about its history.