Porcellanite (shale)
Biogenous sedimentary rock.
This rock sample consists interbedded thin layers of white porcellainite, and organic-rich black shale and chert. Porcellanite
is a hard, dense rock somewhat similar in appearance to unglazed porcelain, similar to chert, but has impurities contain clay and calcerous matter. Organic impurities make the chert dark. This rock formed for plantonic residues possibly far offshore, away from any significant influx of coarser-grained terrigenous sediments.
Beach cobble derived probably from Miocene-age Monterey Shale Formation, Santa Cruz County, CA. |
| https://gotbooks.miracosta.edu/rocks/sedimentary/25.html |
2/2/2021 |
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