Weathered dunite, Newdale, NC

Click on image to enlarge          Photo © Daniel R. Snyder

Above: Weathered dunite, with small grain size and indented grain boundaries resulting from cataclasis and subsequent weathering. All of the blue-green olivine grains clustered at left center go extinct simultaneously, indicatng that they are fragments of a single crystal. Note the dense network of dissolution channels and voids (black). Newdale, Yancey County, North Carolina. XPL digital mosaic. Imaged area 1.3 mm x 3.2 mm.

Below: Optical scan of a freshly-sawn surface of weathered Newdale dunite, same sample as above (NOT same scale). Yellow-orange color is imparted by hematite, disseminated in serpentine layers between and within olivine grains. In the high-magnification view, many of the more robust olivine grains can be seen to retain a light yellowish-green color. Dark grains at lower left are chromite. Dark green grains in cluster at upper left may be remnants of a fragmented hornblende grain. 2400-dpi optical scan. Imaged area 11.4 mm x 17 mm.

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

Talc in weathered Newdale dunite

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

In the above XPL image, a large talc clot (center) is surrounded by weathered olivine grains. The solid black grains at top center, bottom center, and bottom left are chromite. Linear patterns in the lower part of the talc suggest that this part of the talc is partially-altered tremolite/actinolite. Below is a PPL image of the same area at the same scale, showing clearly the chromite and the serpentine meshwork in the dunite. Newdale, Yancey County, western North Carolina. Imaged area 2.7 mm x 4 mm.

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

Webster-Addie ultramafic body, NC - chromite and chlorite in dunite.

Click on the image to enlarge.           Photo: Dan Snyder

A chromite grain (solid black) in the process of altering to chlorite (gray and gray-brown blades). Surrounding (colored) grains are olivine. Chromite is a ubiquitous accessory in most peridotites of the southern Appalachians. The chlorite mineral is kammererite, a chlorite variety unusually rich in chromium and magnesium. Thus, it grows at the expense of both chromite (FeCr2O4), from which it takes chromium, and olivine, from which it takes magnesium and silica. Webster-Addie ultramafic body, Blue Ridge Mountains, Jackson County, western North Carolina. XPL. Imaged area 1.3 mm x 2 mm.