Euhedral, Ca-free beusite (Mn1.5Fe1.5)(PO4)2 coexists with sarcopside and alkali-bearing phosphates within a troilite nodule in the El Sampal IIIA iron meteorite. From single-crystal X-ray data, the structure is monoclinic, P21/c with a = 8.757(3), b = 11.381(4), c = 6.136(1) Å, β = 99.09(2)°. Refinement (R = 0.047) showed the structure to be that of graftonite. The coordination of the M1 site, in contrast to Ca-rich beusite, is nearly sixfold coordinated, as two O atoms are displaced 2.86 and 2.97 Å from the M1 cation. A comparison of graftonite-type structures with different Ca contents in M1 shows a progressive change from eightfold to sixfold, tending to fivefold coordinated M1 as the M1 cation changes from Ca to Mn, Fe to Fe. This illustrates the extreme flexibility of this structure type.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not have access to this content, please speak to your institutional administrator if you feel you should have access.