Lead author is Edward Stolper and his colleagues - including Caltech senior research scientist Michael B. Baker and graduate student Megan Newcombe - examines in detail a 50-centimeter-tall pyramid-shaped rock named "Jake_M" (after MSL surface operations systems chief engineer Jacob "Jake" Matijevic, who passed away two weeks after Curiosity's landing).
The rock was encountered by Curiosity a few weeks after it landed, during its slow drive across Gale Crater on the way toward the crater's central peak, Mount Sharp.
Visual inspection of the dark gray rock suggested that it was probably a fine-grained basaltic igneous rock formed by the crystallization of magma near the planet's surface. The absence of obvious mineral grains on its essentially dust-free surface further suggested that it would have a relatively uniform chemical composition.
For that reason, MSL's scientists decided it would be a good test case for comparing the results obtained by two of the rover's scientific instruments, the Alpha Particle X-ray Spectrometer (APXS) and ChemCam, both of which are used to measure the chemical compositions of rocks, sediments, and minerals.
The APXS analyzes, however, produced some unanticipated results. Far from being similar in its chemical composition to the many Martian igneous rocks analyzed by the Spirit and Opportunity rovers on the surface of Mars or to Martian meteorites found on Earth, Jake_M is highly enriched in sodium and potassium, making it chemically alkaline.
Although Jake_M is very different from known Martian rocks, Stolper and colleagues realized that it is very similar in its chemical composition to a relatively rare type of terrestrial igneous rock, known as a mugearite, which is typically found on ocean islands and in continental rift zones.
--ANI (Posted on 27-09-2013)