CHANNELING A MOTHER ROCK

Mineral Constituents of the Chert Complex

- REBECCA SOLON

Picasso Chert from Burro Creek, AZ, collected by Arizona State University Geology Professor and Author Stan Celestian.

In the March 2020 issue of Rock & Gem, in my article entitled Cherishing Chert: A Mother Rock for the Ages, I discussed the ancient origins of chert as a building block of Earth’s early ocean basins. I illustrated my narrative with two famous formations, the Kaibab Cliffs of the Colorado Plateau and the banded iron formations (BIFs) of Mingus Mountain in the Black Hills region of north-central Arizona.

These ancient deposits crop out at the top of Mingus Mountain and are the source of the hematite and jasp-chert BIFs of the Verde Valley. Chert is a name that is often used interchangeably with another impure opaque variant of chalcedony known as jasper thus the use of the term “JaspChert.” The unique rocks described in this article combine distinguishing characteristics of both varieties and constitute minerals of the chert complex.

CHERT-BASED MINERALS COMBINE ALL ROCK CLASSIFICATION CATEGORIES

The chert-based Kaibab and BIF rocks containing calcium and magnesium-carbonate and iron oxides constitute just a few chert minerals commonly found in Arizona and are now known worldwide. These mineralized rocks establish the complex of chert formations that encompass Earth’s fundamental stratigraphic units as defined by the Geologic Time Scale, and the study of physical geology.