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This rock was about 3-4 inches bigger than a basketball.
When dropped it shattered into a couple large pieces and a lot of small ones.

The inside was marbled yellow (almost like quartz); the marbling was anywhere between 1/4" and 1 inch thick.

I found it in Alberta, Canada, after landmovers went through miles and miles of forest land digging deep into the ground building a new pipeline.

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closed as off-topic by Universal_learner, Peter Jansson, arkaia, Fred, Ash Jul 10 at 18:51

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I'd say it was flint, which is usually associated with limestone. Limestone (calcium carbonate)is a sedimentary rock which forms at the bottom of the sea, and there are often flint nodules (silicon dioxide) in it, especially in the type of limestone known as chalk. Limestone is probably the most abundant sedimentary rock on Earth, so it is more than likely that your pipeline diggers came across some during their excavations. On being struck a sharp blow, flint often shows a conchoid (shell-like) fracture, so try striking glancing blows on it with a hammer and see what type of fractures you get. Flint isn't usually as brittle as you describe it, but I can't think what else t could be.

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  • $\begingroup$ I'd have to disagree with you on this one Michael. That rock is a septarian concretion. The yellow mineral is calcite. The rest of the rock is mudstone. $\endgroup$ – Rokman Jul 17 at 2:52

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