Pyramids & Obelisks
The pyramid is a shape that allows the retention of energies, as a kind of reserve.
The pyramid is the symbol of ascension to the sky. It concentrates and strengthens the properties of each gemstone and eliminates negative energies and chakra blockages.
The trigonal pyramid (4 sides in equilateral triangle) is more specifically intended for the coronal chakra, to make energies rise towards cosmic forces, but it is also usable on all the other chakras.