hexagonal

All of the medals from the Paris Games also feature an 18-gram, hexagonal piece of wrought iron from the Eiffel Tower.

"I wanted to find a particular roofing slate type, which tends to be hexagonal, with a long point on," he said.

The Olympic and Paralympic medals in Paris are being embedded with pieces from a hexagonal chunk of iron taken from the tower.

These molecularly thin 2D organic perovskites are fundamentally different from traditional 3D minerals, they are single crystalline in two dimensions and can be exfoliated as hexagonal flakes just a few nanometres thick -- 20,000 times thinner than a human hair.

These values surpass those of commonly used materials such as silicon dioxide and hexagonal boron nitride.