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Symplectites in Nakhla

The Nakhla meteorite fell in the Nile delta the morning of June 28, 1911. Nakhlites are igneous rocks formed in flows or intrusions on Mars. They are rich in augite and contain a portion of olivine, about 10% in the case of Nakhla itself.

Olivine grains in Nakhla and other nakhlites contain prominent dark flake-like inclusions. These are very thin symplectic intergrowths of augite and magnetite which exsolved from the olivine during cooling from high temperatures. They have specific orientations to the olivine crystal structure.

Nakhla is mostly augite. Here, augite grains are oriented left right. Olivine grains are larger, for example the blue green olivine at top right edge and orange one below it. Sample is 13mm long. Thin section in cross-polarized light (XPL).

 

 

Olivine grains with flake-like inclusions. Field of view (FOV) is 3mm wide, XPL.

 

 

The adjacent olivines in the center display inclusions to the viewer at different angles. FOV= 3mm, XPL.

 

 

The right hand olivine displays the thin inclusions edge on. FOV=0.3mm, XPL.

 

 

The large blue green olivine grain in center has inclusions concentrated in one area. FOV=3mm, XPL.

 

 

Closer. Inclusions are oriented NW-SE. Straight truncations are where the plane of the thin flat symplectite intersects either the top or bottom surface of the 30µ thick sample. FOV=0.5mm, XPL.

 

 

In higher magnification the symplectic texture starts to appear. FOV=0.2mm, plane polarized light (PPL).

 

 

High magnification. FOV=0.08mm (80µ), PPL.

 

 

FOV=0.07mm (70µ), PPL.

 

 

FOV=0.07mm (70µ), PPL.
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