Monipite, MoNiP,

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

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  Fe₂P type structure with a =5.861 Å, c = 3.704 Å, V= 110.19 ų, 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.

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