Phosphates in the Impact Associations of the Chelyabinsk Meteorite
V. V. Sharygin
Geochemistry International, Volume 63, pages 778–799, Published: 23 September 2025
“Na–Fe and Na–Ca–Mg–Fe phosphates were found in the impact melt associations of the Chelyabinsk meteorite (Chebarkul fragment). They drastically differ in composition from phosphates of the initial chondrite (chlorapatite and merrillite). Chladniite Na2.25Ca2.14Mg6.47Fe3.76Mn0.17(PO4)9 and a merrillite-like phase Na1.32Ca6.80Mg2.07Fe0.98Mn0.04(PO4)7 were found in the silicate part in quenched interstitial groundmass between olivine grains; merrillite and chlorapatite are rare in it. The spongy metal–sulfide aggregate in the large vugs and metal–sulfide blebs in the silicate part contain Na–Fe phosphate globules. They consist of sarcopside and graftonite (Fe2+,Mn2+)3(PO4)2, galileiite Na(Fe2+,Mn2+)4(PO4)3, xenophyllite Na4(Fe2+,Mn2+)7(PO4)6, an unidentified Na–Fe phosphate Na2(Fe2+,Mn2+)17(PO4)12, and sometimes chromite-2. Dendritic–skeletal growth of crystals (providing evidence of very rapid quenching) is found in all associations of the impact melt (silicate part, vugs, metal–sulfide aggregate, metal–sulfide blebs, and phosphate globules). The following crystallization sequence is revealed in the Na–Fe phosphate globules: chromite-2 → sarcоpside/graftonite → galileiite → xenophyllite. They are thought to have formed due to the separation of Na–Fe phosphate liquid from homogenous Fe–Ni metal–sulfide melt enriched in Na, P, Cr, and O. The Na–Ca–Mg–Fe phosphates crystallized without involvement of any processes of liquid immiscibility, directly from silicate melt. The paper provides data on the chemical composition and Raman spectroscopy of all studied phosphates and the major minerals of the impact melt associations of the Chelyabinsk meteorite.”
