Shatter Cone
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Shatter cones are rare geological features that are only known to form in the
bedrock In geology, bedrock is solid Rock (geology), rock that lies under loose material (regolith) within the crust (geology), crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface mater ...
beneath
meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or Natural satellite, moon. When the ...
impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters ...
s or underground nuclear explosions. They are evidence that the rock has been subjected to a
shock Shock may refer to: Common uses Collective noun *Shock, a historic commercial term for a group of 60, see English numerals#Special names * Stook, or shock of grain, stacked sheaves Healthcare * Shock (circulatory), circulatory medical emergen ...
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 as
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
, they form an easily recognizable "horsetail" pattern with thin grooves (''
striae Stretch marks, also known as striae () or striae distensae, are a form of scarring on the skin with an off-color hue. Over time they may diminish, but will not disappear completely. Striae are caused by tearing of the dermis during periods of r ...
''). However, the word "striae" should not be used to describe shatter cones, as that is considered misleading. 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 rocks along a fault. This surface is typically striated with linear features, called slickenlines, in the direction of movement. Geometry of slickens ...
. 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 The Slate Islands are an island group in the Inner Hebrides, lying immediately off the west coast of Scotland, north of Jura and southwest of Oban. The main islands are Seil, Easdale, Luing, Shuna, Torsa and Belnahua. Scarba and Kerrera, which ...
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 rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of di ...
*
Coesite Coesite is a form ( polymorph) of silicon dioxide Si O2 that is formed when very high pressure (2–3 gigapascals), and moderately high temperature (), are applied to quartz. Coesite was first synthesized by Loring Coes Jr., a chemist at the ...
*
Lechatelierite Lechatelierite is silica glass, amorphous SiO2, non-crystalline mineraloid. Structure Lechatelierite is a mineraloid as it does not have a crystal structure. Although not a true mineral, it is often classified in the quartz mineral group. Formati ...
*
Shocked quartz Shocked quartz is a form of quartz that has a microscopic structure that is different from normal quartz. Under intense pressure (but limited temperature), the crystalline structure of quartz is deformed along planes inside the crystal. These pla ...
* Stishovite


References


Further reading

* Johannes Baier (2018): ''Zur Entdeckung und Deutung der Strahlenkalke (Shatter-Cones) im Steinheimer Impaktkrater''. In: ''Geohistorische Blätter'', Vol. 29, S. 55–68. * Johannes Baier (2018): ''Ein Beitrag zur Shatter-Cone-Bildung (Steinheimer Impaktkrater, Deutschland)''. In: ''Aufschluss'', 69(6), S. 370–376. * Johannes Baier & Volker J. Sach (2018): ''Shatter-Cones aus den Impaktkratern Nördlinger Ries und Steinheimer Becken''. In: ''Fossilien'', 35(2), S. 26–31. * Volker J. Sach & Johannes Baier (2017): ''Neue Untersuchungen an Strahlenkalken und Shatter-Cones in Sediment- und Kristallingesteinen (Ries-Impakt und Steinheim-Impakt, Deutschland)''. Pfeil-Verlag, München. . {{Impact cratering on Earth Impact craters Impact geology Petrology