Shatter cones are rare geological features that are only known to form in the bedrock beneath meteorite

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 crater ...

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, ...

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.

Morphology

See also

References

Further reading