This is a quote from another website which explains it better than I could.....
According to abundant geological evidence, an asteroid roughly 10 km (6 miles) across hit Earth about 65 million years ago. This impact made a huge explosion and a crater about 180 km (roughly 110 miles) across. Debris from the explosion was thrown into the atmosphere, severely altering the climate, and leading to the extinction of roughly 3/4 of species that existed at that time, including the dinosaurs. Many asteroids of this type are now known; their orbits pass through the inner solar system and cross Earth's orbit. Some of these could potentially hit Earth in the future. Most, but not all are smaller than the one that hit us 65 million years ago.
You can read more for yourself
This really is a rare sample, and one I have spent some time sourcing. If you are in any way intrigued by the cataclysmic events that brought about the end of the Dinosaurs this is a superb opportunity to add it to your collection.
The 4 rock samples you will receive won't be these exact ones, but VERY similar in size and weight.
They will both measure roughly 5mm across
All these samples are accompanied by an A4 full colour signed certificate of authenticity