Nasa's Mars Rover Spirit has delivered its first data on the minerals present in the soil of the Red Planet.
Adirondack's dust-free surface is ideal for grinding
Spirit has used two of its key scientific devices for the first time: its Mossbauer spectrometer and its alpha particle X-ray spectrometer.
The results so far reveal the presence of the mineral olivine, which is a possible product of volcanic activity.
Spirit will now pause to conduct tests on the mineral make-up of the football-sized rock dubbed Adirondack.
Spirit used its science instruments to examine a patch of Martian soil about 3 centimetres (1.2 inches) across.
"There are a couple of surprises that came up when we looked at this data," said Professor Steve Squyres, principal investigator for the science payload.
"Olivine in the Martian soil. What is olivine? It's a mineral, it has silicon, oxygen and iron and magnesium in it. It is a mineral that one finds in igneous rocks: volcanic rocks, lava, basalt.
"It is primarily an igneous rock; it is not something that forms as the result of lots of chemical weathering."
He added that there was a possibility the soil in the Gusev Crater might be very finely ground lava.
"Some people on my team are so surprised to see this olivine that they don't think we're looking at the soil. It's entirely possible that a millimetre down beneath those grains is solid rock.
"There are some people that think we're looking through that fluffy stuff."
The rover analysed the patch of soil in the yellow box
Professor Squyres said the basic elements in the soil were very similar to those identified at the landing sites of the Mars Pathfinder and the Viking missions.
He added that global dust storms over the planet's history could have stirred up material from all over the planet and deposited it globally.
"This stuff could have come from somewhere else. It's going to be very interesting to dig some holes, or to go somewhere else where Mother Nature has dug some holes - in craters," he said.
The rover took pictures of the Martian soil with its microscopic imager, before and after pressing the head of the Mossbauer spectrometer against the grains with a force of around 113 grams (4 ounces).
The images reveal that the spectrometer did not collapse the grains or deform them, suggesting that they were held together by some force.
Professor Squyres also said that sulphates and chlorides may be present in the soil and holding it together like "chemical glue".
"There may be sulphates and chlorides - salts - that are globbing these things together. Now how did they get there? They could have been transported by water, [or] these things could be put out by volcanic processes," he said.
The presence of significant levels of sulphur and chloride in readings from the alpha particle X-ray spectrometer support this hypothesis.
But there were other reasons why these two elements could be present in the soil, Professor Squyres said.
The rover is currently gathering data on the rock Adirondack using the X-ray spectrometer. It will analyse the rock's surface with the Mossbauer spectrometer early on Wednesday GMT.
The scientists are currently deciding whether to use the rover's grinding tool to examine beneath the surface of Adirondack on Wednesday.