Pyroxene grains and pseudomorphs in Josephine serpentinized peridotite.

Click on image to enlarge.          Photo © Daniel R. Snyder

In this specimen,  A few very small remnants of olivine (bright-colored grains) can be seen around the image, but almost all of the olivine has been altered to serpentine. I collected this specimen on the border between the Josephine peridotite and the Onion Camp complex of Yule et al. (2006)*. I decided to call it Josephine peridotite for two reasons: 1. There is little evidence of shearing, and 2. Many large pyroxene grains still persist, and large serpentine pseudomorphs after pyroxene are distributed throughout the specimen. The large gray pyroxene grain at the left side of the image above still appears to be mostly pyroxene, while the broken grain in the center has been altered to bastite-texture serpentine. Hourglass-texture serpentine, probably an alteration product of olivine, occupies the rest of the image. Klamath Mountains, Josephine County, southwest Oregon, XPL. Imaged area 2.7 mm x 4 mm.

In the image below, the white spots on the large hand specimen are reflections from the surfaces of platy pseudomorphs after pyroxene; gray-green grains are pyroxene. Note that there appears to be more remnant pyroxene than pseudomorphosed pyroxene. The brown mesostatis is serpentine. The surface of the small hand specimen has been rough polished, showing dark grains of pyroxene. Lighter gray areas are serpentinized pyroxene grains (pseudomorphs). Scale is in centimeters.

Click on image to enlarge.          Photo © Daniel R. Snyder

*Yule, J. D., Saleeby, J. B., and Barnes, C. G., 2006, A rift-edge facies of the late Jurassic Rogue-Chetco arc and Josephine ophiolite, Klamath Mountains, Oregon, in Snoke, A. W. and Barnes, C.G., eds., Geological studies in the Klamath Mountain province, Californa and Oregon: A volume in honor of William P. Irwin: Geological Society of America Special Paper 410, p. 53-76.

Presque Isle peridotite - full thin section

Click on image to enlarge.          Photo © Daniel R. Snyder

This image shows the texture of the peridotite, in which olivine and pyroxene have been almost entirely pseudomorphed by serpentine, much of which has been replaced in turn by amphiboles. Light-colored areas are carbonate veins. Marquette County, northern Michigan. XPL Macrophotograph. Imaged area 25 mm x 41 mm.