NASA said Thursday that its Mars rover has made an unusual geological find.

The first rock Curiosity inspected from the area near the shiny object, using two different composition-reading instruments, exhibited an unusual composition compared to Mars rocks examined elsewhere, the space agency said. The composition resembled an unusual type of rock found in the Earth's interior, NASA said.

The rock is, "high in elements consistent with the mineral feldspar, and low in magnesium and iron," according to professor Ralf Gellert of the University of Guelph, who helped design some of the instrumentation aboard Curiosity.

This rock, examined by two different instruments aboard the Mars rover, has an unusual composition compared to Mars rocks studied previously, according to the rover team. The red dots are where the Chemistry and Camera (ChemCam) instrument zapped it with its laser on Sept. 21 and Sept. 24. The circular black and white images were taken by ChemCam to look for the pits produced by the laser. The purple circles indicate where the Alpha Particle X-ray Spectrometer trained its view. Courtesy NASA/JPL

"This rock is a close match in chemical composition to an unusual but well-known type of igneous rock found in many volcanic provinces on Earth," said Edward Stolper of the California Institute of Technology in Pasadena, in a statement about the find. "With only one Martian rock of this type, it is difficult to know whether the same processes were involved, but it is a reasonable place to start thinking about its origin."

On Earth, rocks with composition like one examined by Curiosity typically come from processes in the planet's mantle beneath the crust, from crystallization of relatively water-rich magma at elevated pressure, according to a statement from the Jet Propulsion Laboratory at the California Institute of Technology.

The news of the find came a day after the agency said a shiny object seen near Curiosity in a photo, which sparked a flurry of excitement, was likely a piece of plastic from the rover itself.

Curiosity will continue taking pictures of its surroundings as the project team decides the next move. NASA says the rover is preparing to use its onboard lab to do the first detailed analysis of a Martian soil sample. It will also soon move a short distance to the east and use its drill for the first time to take rock samples.

The Mars Science Laboratory is 63 days into a two-year mission to investigate whether conditions may have been favorable for microbial life.

Curiosity landed in an ancient crater in August and started driving toward its first science destination after a month checking out its instruments.