# Difference between "mafic floor" and "olivine-bearing floor" in Jezero crater? (Perseverance landing site)

Figure 3: Main geologic units within Jezero crater shown on a basemap constructed from images from the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter (MRO). Blue circle shows the location of the Perseverance rover landing ellipse.

The image above shows the labels "mafic floor" and "olivine-bearing floor" in Jezero crater along with the Western delta and Perseverance's landing ellipse.

It looks like the Octavia E. Butler1 landing site is somewhere between the two labels, and I'm not sure if there is a distinct border between the two or not.

Question: What is the difference between the "mafic floor" and "olivine-bearing floor" in Jezero crater? Are they exclusive or overlapping designations? Is there a borderline? In which did Perseverance land?

This image shows two possible routes (blue and purple) to the delta.

• Comments are not for extended discussion; this conversation has been moved to chat. Mar 8 at 13:42

TL, DR: Olivine is a specific type of mafic or ultra-mafic mineral that is specifically identified in some parts of the overall mafic floor of the crater. The olivine is seen in specific areas of which the indicated "olivine-bearing floor" is most prominent.

Mafic: More than just olivine

In mineralogical terms, "mafic" is a more general term than "olivine", the latter being a specific type of mafic mineral. As shown in the diagram below, mafic minerals include predominantly olivine and also pyroxene, the latter having slightly more silica content and thus being slightly less "mafic".

In chemical terms olivines have the formula $$\text{(Mg, Fe)}_2\text{SiO}_4$$ which represents the lowest possible molar ratio of silica to metal oxide in a silicate because each silicon atom is "saturated" with extra oxygen atoms from the metal oxide component, thus breaking up the silicate network into discrete $$\text{SiO}_4^{4-}$$ tetrahedra. Pyroxene more closely resembles other silicate minerals in having less metal oxides relative to the silica content, and thus preserving the polymeric silicate networks.

### Jezero Crater

The mineral classification of the various regions of Jezero crater is based data from visible and near-IR spectroscopy of the surface by Horgan et al. [1]. The floor of the crater contains the bulk of observed mafic matter similar to the Gale Crater discussed in this answer. The mafic matter exposed on the surface consists of a mosaic of olivine and pyroxenes (compare with the chart above), with a prominent olivine (red) region near the western edge where the olivine-bearing floor is identified.

Image from Ref. 1, Figure 6.

Reference

1. Briony H.N. Horgan, Ryan B. Anderson, Gilles-Dromart, Elena S. Amadord, Melissa S. Ricee, "The mineral diversity of Jezero crater: Evidence for possible lacustrine carbonates on Mars", Icarus 339, 15 March 2020, 113526.

• Great post; thanks for the edit!
– uhoh
Mar 7 at 15:53