Main task of NASA's Opportunity Mars rover is to study the surface of the planet. The rover has found some very unusual rocks and minerals on a hill overlooking a site 'Marathon Valley'.

Opportunity Project Scientist Matt Golombek, of NASA's Jet Propulsion Laboratory, was of the view that they drove to the edge of a plateau in order to see down in the valley. It was then that they found the rock, big and dark-grey.

"We checked one and found its composition is different from any ever measured before on Mars. So, whoa! Let's study these more before moving on", said Golombek. NASA officials affirmed that they evaluated the rocks and found them to be rich in silicon and aluminum.

Due to this, these stones are quite different from the ones that have been found by Oppurtunity or its twin rover Spirit. In January 2004, Spirit and Oppurtunity were sent to Mars in order to find water activity on the planet.

The researchers said that the rovers have found many such evidences that have helped the researchers to understand the Red Planet and its history. The golf-cart-size rovers are also quite famous because of their longevity.

Their initial missions were set at just three months but until 2010, Spirit kept on exploring Mars. On the other hand, Oppurtunity is still exploring.