High Calcium Pyroxene (HCP) in ultramafic rocks on Mars (Jezero Crater) ?
Norgert Brügge, Germany
The rover "Perseverance" landed on Mars in Jezero Crater on February 18, 2022 and has now carried out a number of investigations on the rock formations encountered. It is exclusively ultramfic bedrock (with a high content of hornblende and olivine) and stratified ash deposits in the area of the delta in the crater.
A recurring feature are white-colored mineral parts, both in the magmatic bedrock and in the ash deposits, which are not sandstone* of fluvial origin. The white components have so far been interpreted as secondary formed salts or gypsum, but this is very unlikely. This statement is based on the spectrographic detection of sulfur. These "salts" (or so) were not pulverized by an abrasion. The components therefore appear to have a hardness that can indicates an accumulation of primary grown crystals in a melt.
In the ultramafic bedrock of Jezero Crater, these accumulations occur as patches in the matrix, in the ash deposits they look like spatters, but can also occur in bands or as blobs.
The white color document the high calcium content, which suggests that it could be the mysterious High Calcium Pyroxene (HCP), which has so far only been detected on asteroids, the Earth's moon and in meteorites. So far, there are no credible statements from NASA about this white component on Mars. It seems to be difficult.
The isolating occurrence in rocks and ash remains a mystery. It is possible that this is a strongly carbonatic melt (Ca2Si2O6) that occurs as an admixture in the otherwise ultramafic magma or that entered the ash deposits in pure form as volcanic lava. Small volcanic bullets have also been found in which an aerodynamically segregated arrangement of the white components is visible. Uncrystallized lava boulders are also found, in which, next to holes of decomposed olivine-phenocrysts, the white parts on the smooth surface can be clearly seen.
* The stratified deposits in the delta are meanwhile been unmasked as layers of ash. They are the moraine of a former dry ice glacier and were transported and stacked as large blocks. Tilts, gaps and internal disruptions bear witness to this.
1. Solidified ash deposits
Other prominent bright components in the ash deposits at the delta scarp:
Small volcanic bullets with aerodynamic segregation of white components:
3. Ultramic bedrock