Euhedral crystal in NWA Achondrite - What is it? • Sunday, Aug 3, 2009
There is a large (~4mm), shiny, iridescent crystal in the broken face of this achondrite meteorite from NWA. Is this Labradorite?

The achondrite specimen has shipped out Saturday, August 8 to HIGP at the University of Hawaii at Manoa in response to Drs Jeff Taylor and Gary Huss' invitation to analyze the meteorite.

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Update: Thursday, August 13, 2009
From Dr Jeff Taylor, UH Hawaii Institute of Geophysics & Planetology (HIGP)

A report about our findings from a quick Raman study of the NWA sample is attached. In contrast to what I told Ken on the phone yesterday, the iridescent mineral is augite, not orthopyroxene. It is certainly not plagioclase. The main phase appears to be olivine, which would make this more likely to be a brachinite, which are typically 90-95% olivine with some augite and minor phases. We'll put it in the SEM next, which I hope will happen next week. We'll check phase compositions, and verify that the augite has high Ca and hence is not orthopyroxene. It will also tell us roughly the Fe/Mg in the phases. As I recall, brachinites have pretty high Fe--something like Fo(65)--but I'd have to check that out more thoroughly.

Achondrite with iridescent crystals

Achondrite with crystals indicated

Video of euhedral crystals in achondrite

Photomicrographs from UH Hilo
I met with Dr Ken Hon of UH Hilo Geology, and introduced my rock to him. Intrigued, Ken offered to take some photomicrographs of the crystal with his nifty setup. We'll be sending pictures to Jeff Taylor and Gary Huss over on Manoa to scrutinize before sending the stone out to them for analysis. Note parallel striations in crystal - not twinning.

One of the spectra taken of the large crystal that looks like it has iridescence and could be labradorite. It actually is augite—compare to augite (right, at different scales) and the labradorite (right).

Labradorite spectrum differs from that of the crystals in the NWA sample.

The other main phase is Olivine. In fact, olivine appears to be more abundant that augite.

This is typical of the dark grains in the rock. It matches olivine—see right.

Other things in the rock. The only other phases identified appear to be either amorphous (especially the smooth surface, which looks like either weathered fusion crust or desert varnish). We did not make a thorough study of the rock to characterize all phases present.

Conclusion, so far. Olivine is more abundant than augite, making this likely to be a brachinite, not a lodranite (the latter are composed of olivine and orthopyroxene, plus metallic iron).