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It looks to me like a breccia, where crystals of some mineral, perhaps tourmaline or olivine, have been scattered in a thin layer on the sea bed or the bed of a lake, and become welded together by minerals precipitated from the water. That would explain the thinness of the specimen and its straight,linear shape. Maybe a volcanic eruption in ancient times ...


This is a quartz vein that has strong microfracturing and moderate hematite alteration. The fractures are filled in with hematite-rich fluids, which accounts for the red color. This is a good example of fluids filling in microfractures, which is a very common process in rock mechanics. The fracture-filling process occurs at depth within the earth's crust ...


This is a quartz vein that has moderate hematite alteration. There is no feldspar in this sample.


Agree with the first reply. It is flint. Also known as chert. The composition is Silica Dioxide (SiO2) which is the same composition as quartz. You'll get all different kinds of SiO2 out there with varying names based on the structures in the rock. Agate, chert, calcedony for example.


It looks to me like a type of flint. Flint nodules are found in chalk and some types of limestone. By banging them with a hammer, you should be able to strike off curved chips with sharp edges. Fractures of flint typically show a conchoid (shell-like) curve. The interior of a flint nodule is brownish, with a glassy texture, but the exterior is often white ...

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