Discovery of a fascinating “mineral flower” on Mars

A few days ago, the Curiosity roverstill active on Mars, took a photography very strange: on the sandy ground beaten by the winds martians stands a tiny concretion flower-shaped mineral. Barely 1 cm wide, the concretion has several arms, connected at the base.

However, this is not the first time that Curiosity has photographed this kind of formation. For scientists, they result from a diagenetic process, which means that they are the result of a rearrangement in situ of minerals, leading to the growth of a new crystal. The formation of this type of structure is notably associated with the presence of water saturated with sulphates.

A Martian analogue of our sand roses

In this sense, it could be the Martian analog of our roses from the sands. The appearance of the formation is indeed reminiscent of an evaporitic concretion. On Earth, evaporites are sedimentary rocks resulting from deposits which precipitate during the process of evaporation of a liquid supersaturated with chlorides or sulfates (brine). Rock salt is the best known evaporite, but gypsum or anhydrite are also part of this class of minerals. Evaporites therefore generally form in shallow basins, subject to strong evaporation and a deficient hydrological regime, such as lagoons or the dead Sea.

The well-known sand roses are formed under specific conditions. These magnificent rocks color orange are crystallizations of gypsum in a generally sandy environment. Sand roses are therefore not formed in quite the same way as gypsum in the middle. lake. Gypsum crystals grow even inside an unconsolidated medium (such as sand orclay), soaked with a water table rich in calcium sulphate. As the evaporation progresses, the water table concentrates in ions, until the saturation allows the crystallization of the minerals. The crystals grow by pushing the sand around them. We thus find the roses of the sands in the desertsburied under a few meters of sand.

A small mineral flower unearthed by erosion

A similar process could be the origin of the thin Martian concretion named Blackthorn Salt. Previous studies of similar concretions show that the crystals would have grown within the soil. But how to explain their presence on the surface today? Simply by the process of erosion. Over time, the Martian winds abraded the rock, until they brought to light these small concretions. More resistant to erosion due to its nature, this concretion is now found on the ground, like a small mineral flower with the surface of mars.

On another Martian site studied by Curiosity, the composition of this type of concretion was analyzed using instruments ChemCam/LIBS and APXS. It appears, for this site at least, that the concretions are particularly enriched in magnesium (Mg) and in several varieties of sulfide (S). The chemical composition would be mainly MgSO_4, what differentiates these concretions from terrestrial gypsum, of composition CaSO₄.

This type of concretion thus gives a lot of information on the past environment of Mars, and in particular on the presence of water in the form of brine in its basement.