Concretions are postdepositionally cemented areas within sedimentary rocks that occur as spheres, disks, tubes, botryoidal aggregates, or have an irregular lumpy shape. The cement forms through precipitation from pore water and is usually composed of carbonate (e.g., calcite, siderite), sulphate (e.g., gypsum), silica (e.g., chert), or iron oxide (e.g., hematite). Nodules have a similar origin, but instead of cementing the pre-existing sediment in place, they substitute the particles through relocation or dissolution.
The Mars Exploration Rover Opportunity was the first to discover concretions on Mars, the so-called ‘blueberries’, which are cemented by hematite (Squyres et al. 2004). The Mars Science Laboratory Curiosity has discovered light-toned concretions within mudstones at Gale crater, which possibly are cemented by sulphates (Grotzinger et al. 2014). The occurrence of concretions on Mars is insofar of interest to astrobiologists as they indicate the former presence...