Twinned Clinopyroxene in Greenstone

Click on image to enlarge.         © Daniel R. Snyder

Twinned clinopyroxene in greenstone no. 108, cobble from glacial gravel, southeastern Michigan, likely provenance northern Ontario. XPL. Imaged area 0.5 mm by 8 mm. (10x objective).

The extinction angle for this and similar crystals in the specimen is 42 degrees. A helpful viewer of this blog suggested that this might be pigeonite. However, after digging deeper into the characteristics of pyroxenes, I found that pigeonite doesn't occur in metamorphic rocks.

Here's an optical scan of a rough-polished section of the hand specimen. Imaged area 11 mm by 17 mm.

Texr