Monipite, MoNiP,

a new phosphide mineral in a Ca-Al-rich inclusion from the Allende meteorite


Chi Ma, John R. Beckett, George R. Rossman
Division of Geological and Planetary Sciences
California Institute of Technology
Pasadena, CA 91125, USA


abstract

Monipite (IMA 2007-033), MoNiP, is a new phosphide mineral that occurs as one 1 2 mm crystal in a Type B1 Ca-Al-rich inclusion (CAI) ACM-2 from the Allende CV3 carbonaceous chondrite.  It has a SG Fe2P type structure with a =5.861 , c = 3.704 , V= 110.19 3, and Z = 3. The calculated density using our measured composition is 8.27 g/cm3, making monipite the densest known mineral phosphide.  Monipite probably either crystallized from an immiscible P-rich melt that had exsolved from an Fe-Ni-enriched alloy melt that formed during melting of the host CAI or it exsolved from a solidified alloy.  Most of the original phosphide in the type occurrence was later altered to apatite and Mo-oxides, leaving only a small residual grain. Monipite occurs within an opaque assemblage included in melilite that contains kamiokite (Fe2Mo3O8), tugarinovite (MoO2), and a Nb-rich oxide ((Nb,V,Fe)O2), none of which has previously been reported in meteorites, together with apatite, Ni2Fe metal, and vanadian magnetite.



MoNiP

Back scattered electron image showing monipite and its associated minerals. Chi Ma SEM image.