Ok, to summarise

1. The crystal shape of magnetite is isometric, and is close to but not exactly two connected Great Pyramid shapes.
2. The GP height of perimeter/2 pi (with error 0.02%) means an imaginary GP octahedron in the shape of crystal magnetite has height of perimeter/pi
3. We do not know if the Egyptians used this ratio on purpose or by accident
4. Evidence from the bedrock beneath the pyramid suggests presence of anything at a supposed subterranean capstone 'as above so below' is purely fanciful

Many thanks for assistance in clarifying this material.

Robert Tulip