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Disharmonic folds in gneiss. Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.

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Flint is a hard, tough chemical or biochemical sedimentary rock that breaks with a conchoidal fracture. It is a form of microcrystalline quartz that is typically called Chert by geologists. It often forms as nodules in sedimentary rocks such as chalk and Marine Limestones.

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Breccia is a clastic sedimentary rock that is composed of large (over two millimeter diameter) angular fragments. The spaces between the large fragments can be filled with a matrix of smaller particles or a mineral cement which binds the rock together. The specimen shown above is about two inches (five centimeters) across.

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What to Know About Sedimentary Rocks

About Sedimentary Rocks By Andrew Alden, About.com Guide

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What to Know About Sedimentary Rocks

What to Know About Sedimentary Rocks: Tilted beds of chert and mudstone

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