We talk about water on Mars all the time but the history of volcanism on Mars is another thing that we are  trying  to understand.What kinds of rocks have been forming over the planet's history? We thought that it was a pretty easy answer, but we're now joining the emerging chorus saying things may be a little bit more diverse on Mars, as they are on Earth.

The location of the feldspar also provides an explanation for how granite could have formed on Mars. While the magma slowly cools in the subsurface, low density melt separates from dense crystals in a process called fractionation. The cycle is repeated over and over for millennia until granite is formed. Granite or its eruptive equivalent rhyolite is often found on Earth in tectonically active regions.

Earlier this year, the Mars Curiosity rover surprised scientists by discovering soil with a composition similar to granite. No one knew what to make of the discovery because it was limited to one site on Mars.

Large amounts of a mineral found in granite called feldspar were found in an ancient Martian volcano. Minerals that are common in basalts rich in iron and magnesium are nearly completely absent here.
The volcano is dust-free making it ideal for the study. Most volcanoes on Mars are blanketed with dust but this volcano is being sand-blasted by some of the fastest-moving sand dunes on Mars, sweeping away any dust that might fall on the volcano.

http://www.sci-news.com/space/science-granite-mars-01557.html