A conchoidal fracture is produced when some types of fine-grained mineral, such as obsidian and flint, are broken. These minerals were widely used in the stone age to make sharp tools. They occur also in amorphous solids such as glass. A fracture is the separation of a body into two, or more, pieces under the action of stress. ... A crystallite is a domain of solid-state matter that has the same structure as a single crystal. ... Minerals are natural compounds formed through geological processes. ... Top stone is obsidian, below that is pumice and in lower right hand is rhyolite (light color) Obsidian is a type of naturally occurring glass, produced from volcanoes when the right kind of lava cools rapidly, e. ... Pebble beach made up of flint nodules eroded out of the nearby chalk cliffs, Cape Arkona, Rügen Flint (or flintstone) is a hard, sedimentary cryptocrystalline silica rock with a glassy appearance. ... Stone Age fishing hook. ... An amorphous solid is a solid in which there is no long-range order of the positions of the atoms. ... The physics definition of a glass is a uniform amorphous solid material, usually produced when a suitably viscous molten material cools very rapidly, thereby not giving enough time for a regular crystal lattice to form. ...

Conchoidal fractures often result in a broken, curved surface that resembles the rippling, gradual curves of a mussel shell, the Greek word for which conchoid derives. A swelling appears at the point of impact called the bulb of percussion. Shock waves emanating outwards from this point leave their mark on the stone as ripples. Other conchoidal features include small fissures emanating from the bulb of percussion.

They are defined in contrast to the faceted fractures seen in single crystals such as semiconductor wafers and gemstones, and the high-energy fracture surfaces desirable in most structural applications. As conchoidal fractures can be produced only by mechanical impact, rather than frost cracking for example, they can be a useful method of differentiating prehistoric stone tools from natural stones. Facets are flat faces on geometric shapes. ... Quartz crystal A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... See Wafer (cooking) for the original meaning of the word. ... A gemstone is a mineral, rock (as in lapis lazuli) or petrified material that when cut or faceted and polished is collectible or can be used in jewellery. ...

Such fractures form the basis of flint knapping, since the shape of the broken surface is controlled only by the stresses applied, and not by some preferred orientation of the material. This property also makes such fractures useful in engineering, since they provide a permanent record of the stress state at the time of failure. A flintknapper is an individual who manufactures stone tools through the process of lithic reduction. ... Stress has different meanings in different fields: Stress in physics, see also pressure. ... Categories: Move to Wiktionary | Standards stubs | Networks | Failure ...

See also: Hertzian cone. A Hertzian cone is cone of force that propagates through a brittle, amorphous or cryptocrystalline solid material from a point of impact, eventually removing a full or partial cone; this result is familiar to anyone who has seen what happens to a plate-glass window when struck by a small...