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Shatter cones are rare geological features that are only known to form in the
Shatter cones are rare geological features that are only known to form in the bedrock
In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet.
Definition
Bedrock is the solid rock that underlies looser surface material. An exposed portion of bed ...
beneath meteorite
A meteorite is a rock (geology), rock that originated in outer space and has fallen to the surface of a planet or Natural satellite, moon. When the original object enters the atmosphere, various factors such as friction, pressure, and chemical ...
impact crater
An impact crater is a depression (geology), depression in the surface of a solid astronomical body formed by the hypervelocity impact event, impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal c ...
s or underground nuclear explosions. They are evidence that the rock has been subjected to a shock with pressures in the range of .
Morphology
Shatter cones have a distinctively conical shape that radiates from the top (''apex'') of the cones repeating cone-on-cone in large and small scales in the same sample. Sometimes they have more of a spoon shape on the side of a larger cone. In finer-grained rocks such aslimestone
Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...
, they form an easily recognizable "horsetail" pattern with thin grooves ('' striae'').
Coarser grained rocks tend to yield less well developed shatter cones, which may be difficult to distinguish from other geological formations such as slickensides
In geology, a slickenside is a smoothly polished surface caused by frictional movement between Rock (geology), rocks along a Fault (geology), fault. This surface is typically Striation (geology), striated with linear features, called slickenlines, ...
. Geologists have various theories of what causes shatter cones to form, including compression by the wave as it passes through the rock or tension as the rocks rebound after the pressure subsides. The result is large and small branching fractures throughout the rocks.
Shatter cones can range in size from microscopic to several meters. The largest known shatter cone in the world (more than 10 metres in length) is located at the Slate Islands in Terrace Bay, Ontario, Canada. The azimuths of the cones' axes typically radiate outwards from the point of impact, with the cones pointing upwards and toward the center of the impact crater, although the orientations of some of the rocks have been changed by post-cratering geological processes at the site.
See also
*Breccia
Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or Rock (geology), rocks cementation (geology), cemented together by a fine-grained matrix (geology), matrix.
The word has its origins in the Italian language ...
* Coesite
Coesite () is a form (polymorphism (materials science), polymorph) of silicon dioxide (silicon, Sioxide, O2) that is formed when very high pressure (2–3 gigapascals), and moderately high temperature (), are applied to quartz. Coesite was first ...
* Lechatelierite
Lechatelierite is silica glass, amorphous SiO2, non-crystalline mineraloid. It is named for Henry Louis Le Chatelier.
Structure
Lechatelierite is a mineraloid as it does not have a crystal structure. Although not a true mineral, it is often clas ...
* Shocked quartz
* Stishovite
Stishovite is an extremely hard, dense tetragonal form ( polymorph) of silicon dioxide. It is very rare on the Earth's surface; however, it may be a predominant form of silicon dioxide in the Earth, especially in the lower mantle.
Stishovite w ...
References
Further reading
* Baratoux, D.; Reimold, W.U. (2016). "The current state of knowledge about shatter cones: Introduction to the special issue", ''Meteoritics & Planetary Science'', Volume 51, Issue 8, Special Issue: Shatter Cones—Nature and Genesis, pages 1389–1434,External links
* {{Impact cratering on Earth Impact craters Impact geology Petrology