What are some isolated holey boulders on Mars ?
-- Iron meteorites or Lava bombs --

Norbert Brügge, Germany
Dipl.-Geol.

Far to the northeast of the landing site of the rover "Perseverance", in a structurally flat area of the Utopia Planitia, the landed Chinese rover "Zhurong" took the first and, for a geologist, very informative photos.

It is ironic, the same vesicular boulders lie on the ground as at the landing sites of "Perseverance" in Jezero Crater and even further northeast of the lander "Viking-2". The rovers "Curiosity", Opportunity" and "Spirit" have also found these stones. They signal an igneous parent rock with phenocrysts of olivine. The decomposed olivine was lost, but sometimes still retained as residue in the holes.

The groundmass of some such holey stones is sometimes in an almost vitreous stage. It means that the magma cooled down quickly, so that hardly any crystallization could take place. These almost vitreous stones are certainly NOT meteorites, but lava bombs. The former pheocrysts of olivine in the holes were already a primary component of the lava. This also applies for occasional occur reflective hornblende crystals.

The result of APXS investigations that they are iron meteorites is very doubtful. These stones are not made of iron, even if the habitus and the false colors suggest it. The reported Fe-peaks in spectrograms can be explained by the prevalence of hornblende.

Six "meteorites" were discovered by Opportunity (named "Heat Shield", "Block Island", "Ireland", "Mackinac Island", "Oileán Ruaidh" and "Shelter Island"). Two similar rocks were identified by the Spirit rover (named "Allan Hills" and "Zhong Shan"). Similar rocks has been identified by the Curiosity rover (named "Lebanon-A/B/C", "Egg rock" and "Ames Knob").

But there are several other candidates of these so named meteorites. Widespread, and in a not vitreous and partly heavily weathered state, they can be clearly identified as ultramafic hornblende-olivine-rich rocks (e.g. Rover "Perseverance").

Photos that speak for themselves

Rover Opportunity (2004 - 2018)

                              

"Heat Shield"


                       

"Block Island"


 


 


 

"Mackinac Island"

"Oilean Ruaidh Island"

"Shelter Island"

Rover Perseverance (2021  ->)

Rover Curiosity (2012  ->

           

"Lebanon"

  
       


"Egg rock & Ames Knob"

Two further candidates

Rover Zhurong  (2021  ->)

              

Rover Spirit (2004 - 2010

Lander Viking-2 (1976 - 1980