Groundmass minerals (replacing pyroxene) forming around well-defined nucleii in greenstone.

Click on image to enlarge.      © Daniel R. Snyder

Above: Neocrystallization of mesostasis (groundmass) minerals around well-defined nucleii.  Note how boundaries of replacement mineral grains iform a subtle mosaic pattern in the same area as the linear pattern of remaining pyroxene structure, which is accentuated by green stringers of chlorite. (center and right). Older mesostasis is on left. Greenstone no. 97, cobble from glacial gravel, southeastern Michigan, provenance likely northern Ontario. PPL. Imaged area 0.13 mm by 0.2 mm (40x objective)

Click on image to enlarge.      © Daniel R. Snyder

Above: XPL. Imaged area 0.5 mm by 0.8 mm. (10x objective). Remnants of pyroxene are yellow-green; altered pyroxene is light brown; dark brown and gray grains are mesostasis. Area covered by 40x image (top of this post) is outlined in white.

Click on image to enlarge.      © Daniel R. Snyder

Above: PPL. Imaged area 0.5 mm by 8 mm. (10x objective0. Area covered by 40x image (top of this post) is outlined in white.

 

Click on image to enlarge.      © Daniel R. Snyder

Above: PPL Imaged area 0.25 mm by 0.4 mm (20x objective). Only the upper three-quarters of the 40x image, outlined in white, is included in this view.