Shatter cone

In short

Shatter cones are cone-shaped fractures that the shock wave of a large meteorite or asteroid impact leaves in rock, their surfaces covered with fine grooves fanning out from the tip. They range from a few centimetres to a few metres in length. They are one of the few signs visible to the naked eye that show a place to be an impact structure. The cone itself is Earth rock; it is not a meteorite.

Photos

How to recognise it

1. 1

   The surface is covered with fine, rounded grooves that fan out from the tip of the cone. In fine-grained rocks the pattern looks like a horse’s tail. Fully developed cones are rare; they are more often seen nested or side by side in clusters.

2. 2

   The tips of the cones mostly point towards the impact point, but irregular orientations are also common. To find the direction of the impact you also have to check whether the rock has been tilted since.

3. 3

   Where it was found matters: shatter cones occur only in and around known impact structures. A grooved, cone-like stone found on an ordinary outcrop is usually not a shatter cone.

4. 4

   A geologist confirms the impact origin: other traces of shock in the same rocks, such as planar deformation lines in quartz grains, support it.

Myths and misconceptions

• MythAny cone-shaped, grooved rock is a shatter cone.

  FactSedimentary structures unrelated to impacts, such as cone-in-cone structures, can look similar; they form as calcite grows while sediments are buried, and have a fibrous internal structure. Shatter cones are the product of very high, instantaneous stresses and occur only in and around impact structures.

• MythEvery impact crater has shatter cones; no cones means no impact.

  FactCones form in rocks where the impact’s shock wave stayed strong enough; they do not occur in craters smaller than a few kilometres across, and even in large structures they do not develop in every rock. A shatter cone is evidence of an impact, but their absence does not show that there was none.

Did you know?

Where is it found?

• Steinheim Basin, Baden-Württemberg, Germany · Type localityThe type locality of shatter cones: they were first described here in 1905, when they were attributed to a “cryptovolcanic” (hidden volcanic) explosion. The crater, famous for its cones in Jurassic limestone, is 3.8 km across, about 14 million years old, and lies about 40 km west of the Ries crater.
• Ries crater, Nördlingen, Bavaria, Germany · Known localityShatter cones occur in this crater, about 24 km across; the same impact also created the moldavite tektites.
• Sudbury Basin, Ontario, Canada · Major depositAn impact structure 130 km across and about 1.85 billion years old. Shatter cones have been reported up to about 15 km from the edge of the melt sheet, and their tips point towards the centre of the basin.
• Vredefort Dome, Free State, South Africa · Major depositAn impact structure about 2.02 billion years old and one of the largest known (170–300 km across when formed). Shatter cones occur up to about 90 km from the centre; Dietz and Hargraves found them in 1961 and so confirmed the structure’s impact origin. It has been a UNESCO World Heritage Site since 2005.
• Slate Islands, Lake Superior, Ontario, Canada · Known localityThe centre of an impact structure about 32 km across. One of the largest shatter cones in the world, about 9 m long, is here. The islands are a provincial park, reached only by boat or floatplane.
• Charlevoix, Quebec, Canada · Known localityAn impact structure about 54 km across and about 450 million years old. The discovery of numerous shatter cones led to its impact origin being recognised in 1965.
• Kentland, Indiana, USA · Known localityAn impact structure about 13 km across. Shatter cones and deformed bedrock revealed its impact origin, and fine cones in dolomite are known from the quarry. The quarry is still being worked today.

Locations are approximate to protect sites. Red dots mark places in Türkiye. Open in the big map →