© 2003 by the Center For Social Research, Parkland College
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Cobden Chert is recovered from the St. Louis Formation, as is Dongola. The difference between it and Dongola is the brown tones of Dongola's matrix.
The texture is fine.
Luster tends to be glassy.
Against a dark gray to blue-black background will be a series of concentric bands of yet darker material.
Fossils are uncommon.
Structural attributes will include: occasional and widely spaced microscopic voids some of which will be lined with iron oxide; the occasional expression of druse; and the occasional oolite.
Cobden Chert is not typically heat treated.
The illustrated specimen was recovered from an erosional feature in the north half of Section 35, two miles west of the the village of Cobden, Union County, Illinois.
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