Magnesite in dunite

Click on the image to enlarge.           Photo: Dan Snyder

A cluster of magnesite (MgCO3) grains in Newdale dunite. Magnesite commonly occurs where peridotites are permeated by carbonate-rich fluids.  Light gray, darker gray, and pale yellow grains at center and left are magnesite. Dark gray grains are at partial extinction; pale yellow grains probably contain a small amount of iron carbonate (siderite) in solid solution. The partially extinct (medium gray) grain at the upper edge of the cluster gives an idea of grain size. Colored grains at bottom, upper left, and right are olivine. Newdale, Yancey County, North Carolina. XPL. Imaged area 2.7 mm x 4 mm. Link to Carolina Geological Society 1997 Guidebook (PDF).