Some of the unusual rocks carry stories about water on Mars. One has hints of long-gone microbes. All tell of a dynamic, complex planet.

Microphotograph of amphibole (brown) and plagioclase (grey-white) minerals present in an adakitic rock from the western Trans-Mexican Volcanic Belt (TMVB) Focus: occurence of adakite rocks and their .

quartz and amphibole." Igneous rocks may be subjected to high heat and pressure, or exposed to fluids that alter their mineral composition. Once their mineral composition changes, the rocks are ...