Saturday, July 21, 2012

Cumulate olivine and interstitial pyroxene in igneous peridotite

Click on image to enlarge.          Specimen: Michael Davis          Photo: Dan Snyder
Olivine (left and right) with interstitial pyroxene (center). Note that opaque secondary mineral(s) occupying fractures in olivine do not extend through pyroxene. Montserate Mountain, San Diego County, California. XPL. Imaged area 1.3 mm x 2 mm.

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 Plane-polarized light image of same area shown above. Fractures appear to end at the olivine/pyroxene border. In the center of the image, the pyroxene is colored by parallel streaks of a red material, probably iddingsite, a late magmatic alteration product of olivine.

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Higher-magnification (10X objective) view of center of previous image. PPL.  Imaged area 0.54 mm by 0.8 mm.

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Higher-magnification (40X objective) view of center of previous image. PPL. Imaged area 0.13 mm by 0.2 mm.

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Optical Scan of remnants of hand specimen after removing material for billet for thin section. Imaged area 54 mm by 51 mm.


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Optical scan of outside of hand specimen minus billet material. Red material appears to be iddingsite. Imaged area 57 mm by 51 mm.



Many thanks to Prof. Michael Davis of the University of California at Riverside for the specimen.