Cone-shaped rock structure with converging fractures. They can range
from 2cm to 2m in size. The fractures are caused by sudden, intense pressure
on the rocks, such as would result from an impact event. Under these circumstances,
the shatter cones point upwards indicating that the impact came from above.
Two photographs are shown, the first one having been caused by explosives.
The second is an example from the Sudbury Impact Crater. Unfortunately
the top has been chipped off this one; otherwise you would be able to see
where the fractures converge into a point.