I even happen to have some of that from a railroad track. Also if it has tiny bubbles in it..its definatly this stuff...its usually attached to other stones because it was molten when it got there. Short of giving you guys a link to learn about chert and how its formed and what it looks like which might not be a bad Idea...I will briefly explain..chert is formed in limestone in a process where silica skeletons of dead marine organisms settled on an ancient sea floor creating thick layers. In time the silica replaced the lime stone under pressure. That pressure was created by more limestone layering on top. So...the chert/ "microcrystaline quartzite" is in the interior of the nodules that are formed. Think of it like an orange..the limestone which is chalky white is on the outside like the Peel or "rind" the solidified chert is in the interior like the pulp. That's what chert looks like...not like the rock above.
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