Yes it is true that this is capstone that once crowned the Black Pyramid at Dashur, Egypt. Only a few have survived into the present day.
Many ancient pyramids used to have a small pyramid-shaped stone on top, called a pyramidion or capstone (like shown in the picture).
These pyramidions were often made of valuable materials like gold or covered with gold. They would shine in the sun and symbolized the presence of the sun god Ra. However, over time, most of these capstones were either stolen or worn away, so many Egyptian pyramids no longer have them.
The ancient Egyptians believed that the pyramidion connected the pyramid to the heavens. It had deep spiritual meaning, symbolizing the link between the world and the sky. This connection was important for the pharaoh’s journey to the afterlife, as they believed the pyramid would help the ruler reach the gods in the heavens.
Many ancient Egyptians believed in the existence of a sacred stone called the Benben stone, kept in a shrine in a temple dedicated to the god Atum in Heliopolis. The term ‘Benben stone’ also refers to the tip of an obelisk or the capstone of a pyramid. In some creation stories, Atum created the universe on top of the Benben stone, which rose from the dark waters.
This sacred relic was once kept in the most important part of the temple in Heliopolis, where Atum was the main god. The original object was lost at some point in history. However, based on pictures, people think it was a tall stone with a rounded top. It’s also been noted that later solar temples had their own Benben stones. For example, the temple of Aten in El-Amarna, built by the 18th Dynasty pharaoh Akhenaten in the 14th century B.C., is said to have had its own Benben stone.