the bedrock
banded chert
SiO2 · not an agate
The tell
THE big one. Hold the thin edge up to the sun. An agate glows, because light passes through the rim. Chert stays dead and opaque no matter how thin the edge is.
Chert bands are fuzzy and roughly parallel. Agate bands are sharp and concentric, following the shape of the cavity they grew in. Most "agates" posted to Michigan rock groups are banded chert, and there is no shame in it.
What it gets mistaken for
The facts
- also calledSiO2 · not an agate
- ageage varies
- where it turns upevery shore · glacial float
- on the chartthe bedrock · 1000 stickers ever
Put it on the shelf
Every stone on this chart is drawn and kiss-cut at three inches. The rarer the stone, the fewer exist: only 1000 banded chert will ever be printed, then the run is retired.
10% of every order goes to the Roscommon County Animal Shelter.