to have seen "fields of skulls" on Mars. See also References External links Science Magazine special issue on MER Opportunity initial results Press releases from JPL relating to Mars spherules: Initial press release, composition results Morphological Investigations of Martian Spherules, Comparisons to Collected Terrestrial Counterparts. Full text PDF. Sedimentary Concretions vs. Impact Condensates: Origin of the Hematitic Spherules of Meridiani Planum, Mars. Full text PDF. Ironstone Concretions - Analogs to Martian Hematite Spherules. Full text PDF. Moqui Marbles relations to Martian Spherules. ScienceDaily.com on Moqui marbles and Martian spherules relations to cyanobacteria and terrestrial stromatolites. Spherules Rocks on Mars