Much of the dirt that Phoenix scooped up and sprinkled on its microscope appeared as a reddish-orange hue that's typical of the Martian landscape.
Zooming in, scientists noticed green particles that could be olivine, a mineral usually associated with volcanic eruptions. The soil also contained round, black glassy specks that could be volcanic glass, said mission scientist Tom Pike of the Imperial College in London.
It's too early to make any generalizations about Phoenix's landing site, but scientists were intrigued by the latest images.
"What we are looking at here is a part of history of Martian soil," Pike said at a news conference in Tucson, Ariz.
The mineral olivine was previously discovered by the rover Spirit, which has been roaming the Martian equatorial plains since 2004.
Since landing near Mars' north pole on May 25, Phoenix has been busy digging shallow trenches in the permafrost and delivering scoopfuls to its microscope and a test oven that is baking and sniffing the soil for traces of the chemical building blocks of life. The first results from the oven experiment won't be available until next week.
