Metamorphosed pyroxene and plagioclase in Litchfield (meta)norite

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

Metamorphosed orthopyroxene (left, bottom, upper right, lower right) and plagioclase (center) in  norite. Pyroxene grains show varying degrees and types of metamorphism. Original linear structure of large pyroxene grain at left is detectable only as a weak lination imparted by dark specks. Plagioclase is more intact, but shows degradation (blurring) of twin lamellae. Mt. Prospect complex, Litchfield County, northwestern Connecticut. XPL. Imaged area 1.3mm x 2mm.

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

Higher-magnification image of replacement product (blue) in large orthopyroxene grain (left side of top photo). XPL. Imaged area 0.5mm by 0.8mm.

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

Higher-magnification (10x objective) image of heavily-altered orthopyroxene grain (lower right corner of top photo). Green areas are remnants of original mineral. Note linear (chain silicate) structure. Also note that small grains of opaque mineral, presumably an iron-oxide mineral, are preferentially concentrated in pyroxene remnants. XPL. Imaged area 0.5mm by 0.8mm.

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

PPL image of above, showing relict lineation and concentration of opaques in pyroxene remnants.

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

Higher-magnification (40x objective) image of cluster of opaques in center of photo above. Note that many of the "opaques" appear to be slightly translucent brown ovals, aligned to the lineation in the pyroxene. PPL. Imaged area 0.13mm by 0.2mm.

Hydrous minerals replacing plagioclase and pyroxene in metabasalt

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

Above: Ophitic-texture pyroxene and plagioclase in a metabasalt are being replaced by hydrous minerals of the greenschist facies. The large orange and brown cluster was a pyroxene grain enclosing the now-corroded plagioclase laths. The pyroxene has been replaced by uralite, a massive amphibole usually composed mainly of actinolite (less commonly of hornblende). The scattered plagioclase laths show varying degrees of replacement by epidote, and probably by other minerals too small to identify. Extensive replament has occurred in the two adjacent, parallel plagioclase laths at right of center (See second image below for greater detail). Greenstone cobble in glacial gravel, southeastern Michigan, Specimen No. 49. Provenance likely northern Ontario. XPL. Imaged area 1.3mm by 2mm.

Below: PPL image of above. Green color of uralite is characteristic of actinolite (as well as hornblende).

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

Below: Higher-magnification image of area right of center in top photo. Note the cluster of small epidote grains that have replaced much of the two adjacent plagioclase laths. The replacement of plagioclase by epidote in this location was likely speeded by a channel between the two grains (visible as a narrow strip of uralite) that provided access by percolating fluids. XPL. Imaged area 0.5mm by 0.8mm.

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

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