After a few dry runs, the Curiosity rover has now put its chemistry set to use at a site called the Rock Garden. For the first time, we've operated an X-ray diffraction system on another planet, telling us something about the structure of the minerals in the Martian soil. The first results tell us the sand the rover has driven through contains some material that wouldn't be out of place near a volcano on Earth.

Curiosity comes equipped with a scoop that lets it pick up loose soil from the Martian surface and drop it into a hatch on the main body. From there, the samples can be directed into a variety of chemistry labs. Yesterday, NASA and the Jet Propulsion Laboratory revealed the first results obtained by the Chemistry and Mineralogy (or CheMin) instrument, the first time anything of this kind has been operated on another planet.

We have a lot of ways to look at the composition of the material on Mars' surface. We can look at the absorption of light by materials (including from orbit), which can tell us a lot about its likely composition. The rover itself has a number of spectrometers, which can also tell us about the chemical composition of rocks, as well as wet and dry chemistry labs.

But CheMin adds a unique capability, in that it tells us something about the structures of the chemicals we detect. It's one thing to know that a sample contains iron and magnesium silicates; it's another thing entirely to know that the mineral is olivine, which has a distinctive structure, and will only form under a limited set of conditions.

CheMin determines structures the same way we do on Earth, using a technique called X-ray diffraction. In this process, high-energy photons bounce off the internal structure of a crystal. The ordered structure of the crystal creates a series of spots that can be used to determine where the atoms it contains are located. Normally, these machines take up whole rooms on Earth, but NASA has found a way to miniaturize one.

This technique works best for single, large crystals that are held in a precise orientation. This isn't something that can be guaranteed with random samples obtained on Mars. Instead, to minimize the chances of obtaining a complex sample, the material is sent through a grating that excludes anything larger than 150 micrometers. Even then, the crystal won't be so homogeneous that it produces a single set of spots; instead, it produces a series of concentric circles extending out from the center of the X-ray beam. The location and intensity of these circles can tell us something about the material being studied.

The results of this first sample indicate dust found at the Rock Garden site is primarily a product of weathered volcanic material called basalt, some of which is more glass-like than crystalline. The crystalline materials present include significant amounts of feldspar, pyroxene, and olivine, all of which can also be found in similar deposits on Earth.

Overall, the rover continues to perform well, and all of its major instruments appear to be operating as planned.