Asteroids and comets have struck the Moon and all the planets including Earth thousands of times over the last 3.5-billion (thousand million) years, leaving impact craters. Over time, on geologically active planets such as the Earth, remains of these craters have for the most part been covered up or eroded away. Nevertheless, long after impact craters have vanished from the landscape, “impactites,” rocks and soil affected, sometimes profoundly so by the impact, may yet remain. The presence of impactites and other geological data has provided evidence of nearly 200 craters on Earth alone.
Robert S. Dietz, who pioneered the concept of seafloor spreading, is credited for making the connection between impact craters and impactites, local or area rocks and soil affected, sometimes profoundly so, by the most violent force on Earth found in nature, that of a large asteroid or comet striking our planet. Dietz studied and collected an impactites known as shatter cones, exactly like this one.
Shatter cones are nothing less than fossilized shockwaves. Their pointy ends face upward toward the direction of impact and their broader bases face down and away. There are fine striations from the point extending down the cone-shaped rock sometimes referred to as "horsetail structures."
They are vaguely like what can occur when a BB hits a glass pane: a cone of glass facing the direction from which the impact came may get popped out, leaving a cone-shaped hole. Of course, impact shatter cones result from forces many billions (thousands of millions) of times greater. An asteroid or comet strikes Earth with enough pressure to liquify rock, making a crater which if large enough sports a central peak. Shockwaves speed many kilometers (miles) beneath the newly-formed crater leaving a few or many thousands of overlapping shatter cones frozen in the hard rock below. In time, the crater becomes covered by strata and dirt. Eventually, the upper layers erode away and as it does the lower rocks with their shatter cones, impact melt glass, fractured rocks and other evidence of cosmic collisions become exposed at the surface.
It was Dietz who proved Sudbury, Ontario, Canada was the site of an ancient impact that occurred nearly 1.86-billion (1.86 thousand-million) years ago which we now know caused mass extinctions including the immediate demise of local stromatolites (fossil algae). Sudbury is today recognized as the location of one of the largest and oldest known impact craters on Earth. The original size is estimated to have been 250-km (155-miles) in diameter.
Offered here is the largest, most massy, and perfect SUDBURY SHATTER CONE I own. It has great signs of shock on both sides. The front is convex, curving outward in a gentle sweep and the back is concave with signs of a negative shatter cone. The rock is incredibly fine-grained and ancient, among the oldest exposed rocks on Earth. This truly museum-quality piece has been flattened over time which is quite normal for Sudbury shatter cones. This ancient aerinite from which it is made is the Canadian Shield, one of the oldest set of exposed rocks on Earth, which range from an age of 2.5 to 4-billion (thousand million) years. It is an extremely heavy piece: 8.89-kilograms (19-lbs, 9-oz.). It is about 36.5 by 23.3 and 12.0-cm thick (14 3/8 x 9 1/8 x 4 7/8-inches thick). Note the tiny one-cm (~3/8-inch) cube for scale is not included.
As for its provenance, I acquired it in trade many years ago from a geologist at Science North and Dynamic Earth in Sudbury, Ontario, Canada. I will include a nice roughly 5.0 by 7.0-cm (2 by 2¾ -inch) printed cardboard descriptive label that states this is from the collection of Richard Dreiser.
Sudbury is town primarily known for the location where many rare minerals and elements are mined. From the late 1800s until the 1960s the skies were dark and full of sulfur dioxide pollution. The city and surrounding areas were full of dead trees, the rocks blackened from decades of ore being smelted. This piece is entirely free from the black patina suggesting it was acquired more recently, likely fresh blasted out of a stone cliff for one of the ongoing construction projects.
This very hard, solid, and heavy specimen, is much too large for passing from hand to hand. It would be the perfect specimen for a professional museum display. It would be a choice specimen for anyone interested in meteorites, ancient rocks, impact craters, and mass extinctions. It would look exquisite set upright and illuminated from the side to accentuate the horse-tail striations, propped in front of a mirror to show the detailed back.