Horoman peridotite (lherzolite), Hokkaido, Japan - symplectite pseudomorphs after garnet.

For a general description of the Horoman peridotite body, see the post of July 2, 2013: "Horoman Peridotite ... - olivine microfabfric".

Symplectite nodules (intergrowths of fine-grained minerals - in this example, spinel and clinopyroxene) are abundant in some layers of the Horoman peridotite complex. Because of their mineral assemblages and bulk chemical composition, these nodules are thought to be pseudomorphs after pyrope garnet.

Click on image to enlarge.          Photo © Daniel R. Snyder
Three large symplectite nodules in the Horoman peridotite body.  Brightly-colored
grains are olivine; gray grains are pyroxenes. XPL. Imaged area 2.7 mm by 4 mm.

Below: Higher-magnification image (10x objective) of a small symplectite nodule.

Click on image to enlarge.          Photo © Daniel R. Snyder
XPL. Imaged area 0.5 mm by 0.8 mm.

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REFERENCES

Morishita, T., 2000, Three-dimensional Microstructure of Symplectite Minerals in the Horoman Peridotite: A preliminary Analysis; Jour. Geol Soc. Japan; 106:11, p. 800-811. (In English with Japanese abstract)

Morishita, T., and Arai, S., (2003), Evolution of spinel–pyroxene symplectite in spinel–lherzolites from the Horoman Complex, Japan; Contrib. Mineral. Petrol; 144, p. 509-22. (In English)

Odashima, N., Morishita, T., Ozawa, k., Nagahara, H., Tsuchiyama, A., and Nagashima, R., (2008), Formation and deformation mechanisms of pyroxene-spinel in an ascending mantle, the Horoman peridotite complex, Japan: an EBSD (electron backscatter diffraction) study; Jour. Mineral. Petrol. Sci., 103, p. 1-15. (In English)