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 an unusual type of rock found on oceanic islands such as Hawaii and St. Helena.
Curiosity's laser was used to zap the football-sized rock, and the rover analyzed the pulverized 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.
The rock, named after a NASA engineer, Jake Matijevic, who died shortly after Curiosity's landing, was also rich in feldspar-like minerals, which provided clues about the rock's history.
"The way in which this type of rock forms ... is like how applejack liquor was made," said geologist Edward Stolper, with the California Institute of Technology.
In colonial times, hard apple cider was put into barrels, and in the winter the liquid would partly freeze. "You'd crystallize out ice and you'd make more and more and more concentrated apple-flavoured liquor," Stolper said.
Magma inside a planet can undergo a similar process.
"You melt the interior and it comes to the surface and, just like the applejack, when you cool it, it crystallizes," Stolper said, adding it takes very particular conditions to produce this type of magma.
