Polyhedral texture in dunite - Scanning Electron Microscope Image

Click on the image to enlarge.  Sample: Michael Velbel; photo: Dan Snyder

Granular (recrystallized) olivine, fractured dunite fragment, Webster-Addie ultramafic body, Jackson County, western North Carolina. Scanning electron microscope (SEM) image (secondary electron image). Magnification 40x.

Thanks to Dr. Michael Velbel, Michigan State U., for the sample, and thanks to Dr. Velbel and NASA for the SEM time. Thanks also to E. Danielewicz for assistance with the SEM.

Polyhedral texture (mosaic texture) in dunite

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

Classic polyhedral mosaic in dunite. This texture results from recrystallization in the solid state, and is common in metamorphic rocks composed mainly of one mineral, such as dunite. Grains tend to have fairly straight sides, and many grain boundaries intersect in triple junctions at approximately 120˚ angles. Webster-Addie ultramafic body, Blue Ridge Mountains, Jackson County, western North Carolina. Macrophotograph, XPL. Imaged area 8 mm x 14 mm.

Buck Creek ultramafic body, NC - chloritization in dunite

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

Advanced stage of chloritization in dunite, Buck Creek ultramafic body, Blue Ridge Mountains, Clay County, western North Carolina. Pratt and Lewis (1905)* described the chloritization of the Buck Creek dunite thus: "In some cases the olivine alters extensively to chlorite, which penetrates the grains generally along cleavage cracks first, though frequently in diagonal directions, in long slender laths, sometimes passing uninterruptedly through two or three grains." XPL. Imaged area 1.3 mm x 2 mm.

Thanks to Dr. Brannon Andersen of Furman University for giving me detailed instructions on reaching this exposure.

*Joseph Hyde Pratt and Joseph Volney Lewis, Corundum and the Peridotites of North Carolina.

Buck Creek ultramafic body - unaltered dunite grading into chloritized dunite

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

Portion of a thin section showing unaltered dunite (left) grading to heavily chloritized dunite (right). Buck Creek ultramafic body, Blue Ridge Mountains, Clay County, western North Carolina. Macrophoto, XPL. Imaged area 10 mm x 20 mm.

Buck Creek dunite - serpentinized and chloritized

Click on image to enlarge. See image below for enlargement of outlined area.

Polished slab of partially serpentinized and chloritized dunite. Buck Creek ultramafic body, Blue Ridge Mountains, Clay County, western North Carolina. Optical scan at 1524 pixels/cm (600 dpi). Original width 3400 pixels, reduced by Blogger to 1600 pixels at maximum magnification. Slab dimensions 8 cm x 14.5 cm. Below is a higher-resolution image (6096 pixels/cm.) of the 3.5-cm-by-3.5-cm area outlined in the larger image.

Click on image enlarge. Click again to get really close up.

Serpentine meshwork in Josephine peridotite

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

Josephine peridotite, partially serpentinized. A component of the Josephine ophiolite sequence. Serpentine meshwork occupies space between grains and along fractures within individual grains. Because serpentine can't accommodate the iron given up by the olivine, this is taken up as hematite, which gives the meshwork its brown color. Josephine County, southwest Oregon. XPL Imaged area 1.3 mm x 2 mm.

Josephine peridotite - hand samples

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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.