Five solids that mathematics allows and no more — and the meanings humans have hung on them.
A Platonic solid is a convex polyhedron whose faces are all congruent regular polygons with the same number meeting at every vertex. Euclid proved there are exactly five. They appear in crystallography, molecular structure, and virus capsid geometry because these arrangements are efficient, not because they are mystical.
Careful: The elemental associations below come from Plato's Timaeus and later esoteric traditions. They are philosophy and symbolism, not physics.
Tetrahedral geometry genuinely appears in chemistry — methane and diamond feature tetrahedral bonding angles. That is a result of orbital geometry, not of the solid 'containing' a moral law.
Activation and transformation.
"What does the Tetrahedron bring to mind for you?"