Josephine peridotite - hand samples

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

Polished section (left) and rough hand sample (right) of Josephine peridotite, a component of the Josephine ophiolite sequence, southwest Oregon and northwest California. Dark grains in polished section (also slightly darker grains in rough hand sample) are orthopyroxene, remainder is olivine. Light areas around edges are weathered rind; white lines are saw marks. Josephine County, Oregon. Scale in centimeters.

Josephine peridotite (harzburgite) - Full thin section in cross-polarized light

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It looks much better close up.                      Photo © Daniel R. Snyder

Josephine peridotite, a component of the Josephine ophiolite sequence. Small, brightly colored grains are olivine, larger grains in shades of gray are orthopyroxene.  Josephine County, southwest Oregon. XPL macrophotograph of entire thin section. Imaged area 18 mm x 38 mm.

Josephine peridotite - digital mosaic

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

In this image: mostly olivine (bright colors) with incipient serpentinization, and a few large (gray) grains of orthopyroxene. Josephine peridotite, a component of the Josephine ophiolite sequence. Klamath Mountains, Josephine County, southwest Oregon. Digital mosaic of four 2x-objective images. XPL. Imaged area 5.1 mm x 7.6 mm.

Josephine peridotite (harzburgite) - pyroxene

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Josephine peridotite (partially serpentinized harzburgite), a component of the Josephine ophiolite sequence. Gray grain at left is pyroxene, large gray grain in center is partially serpentinized pyroxene (bastite texture). Brightly colored grains are olivine. Klamath Mountains, Josephine County, southwest Oregon.  XPL. Imaged area 1.3 mm x 2 mm.

Serpentinite exposure

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Serpentinite exposure adjacent to an extensive occurrence of Josephine peridotite.  Because serpentine can't accommodate the iron in the peridotite protolith, much of this is taken up as hematite, visible as  brick-red layers in the exposure. Road cut opposite Eight Dollar Mountain, Josephine County, SW Oregon. Rock hammer for scale is in the white circle at the bottom of the photograph.

Josephine Peridotite exposure

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

Exposure of Josephine peridotite, base of Eight Dollar Mountain, Klamath Mountains, Josephine County, southwest Oregon.

Deer Lake peridotite - magnetite traces of ancient olivine crystals

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The Deer Lake peridotite, thought to be Proterozoioc in age, is composed entirely of secondary minerals. Here, the outlines of two adjacent olivine crystals - and their internal fractures - have been preserved by stringers of magnetite that separated out when the olivine was serpentinized. The gray masses appear to be carbonate, possibly magnesite, throughout which magnetite grains have been disseminated, giving the gray color. Deer et al.* state that magnesite may be formed if serpentinites undergo low-grade metamorphism where carbon dioxide is available. A few orange and red wisps of anthophyllite or tremolite signal the beginning of another round of alteration. Marquette County, northern Michigan. XPL. Imaged area 1.3 mm x 2 mm.

Deer, W. A., Howie, R. A., and Zussman, J., (1992), An Introduction to the Rock-forming Minerals,  2nd edition, Pearson-Prentis Hall, 685 p.