Subhedral pyroxene in greenstone, No. 48 - full thin section

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

Subhedral pyroxene grains in greenstone. Specimen No. 48, cobble in glacial gravel, southeastern Michigan. Provenance likely northern Ontario. Macrophotograph in cross-polarized light. Imaged area 22mm by 38 mm.

Below: polished cross-section of cobble from which sample was cut. Optical scanner image. Long dimension 6.3cm.

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

Euhedral pyroxene in greenstone (full thin section)

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Euhedral pyroxene crystals in greenstone. Specimen No. 54, cobble in glacial gravel, southeastern Michigan. Provenance likely northern Ontario. Macrophotograph in cross-polarized light. Imaged area 21mm by 39mm.

Actinolite in greenschist

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Tabular and acicular actinolite crystals in greenschist. XPL above, PPL below. Actinolite crystals are light green or dark green, with some zoned crystals and some crystals at extinction (black). Small, irregularly-shaped, multicolored grains at right are epidote. Black and gray mesostasis is mainly quartz. Greenschist pebble, specimen No. 52, from glacial gravel, southeastern Michigan. Provenance likely northwestern Ontario. Imaged area 0.57mm by 0.8mm.

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

PPL image of same area as shown in XPL image. Actinolite is green to blue-green. Small, irregularly-shaped, high-relief grains at right (pale yellow) are epidote, colorless mesostasis is mainly quartz.

Epidote pleochroism in greenschist

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

Epidote in greenschist. In XPL image above, epidote grains are yellow to orange to magenta; some of them, at or near extinction, are dark brown or black. Many of the larger grains show epidote's characteristic oval shape. Small, irregularly-shaped epidote grains in the upper half of the image are partially masked by their high-relief outlines, and also by magnetite grains and finely disseminated magnetite. Imaged area 0.57 mm x 0.8 mm.

The two PPL images below cover the same area as the XPL image above. The characteristic yellow-green to green pleochroism of epidote is evident in these images, which were made with the polarizer at two different angles, approximately 90 degrees apart. Many magnetite grains, clustered above the center of the image and in the upper right corner, are more clearly visible in these PPL images than in XPL.

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

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

Greenschist, No. 1, full thin section in cross-polarized light

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Greeschist pebble from glacial gravel, southeastern Michigan. Provenance likely northwestern Ontario. Macrophotograph in cross-polarized light. Long dimension of imaged area 36mm.

Greenschist, No. 52 - full thin section in cross-polarized light

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

 

Full thin section of greenschist, specimen No. 52. Cobble from glacial gravel, southeastern Michigan. Provenance likely northwestern Ontario. Macrophotograph in cross-polarized light. Long dimension of imaged area 40mm.

Archean greenstone, No. 92

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Archean greenstone collected from outcrop,  Haviland Bay, Ontario (East end of Lake Superior). XPL. Imaged area 1.33mm by 2mm.