Polymorphism can lengthen further than pure symmetry articles. The aluminosilicates are a bunch of a few minerals – kyanite, andalusite, and sillimanite – which share the chemical formulation Al2SiO5. Kyanite is triclinic, even though andalusite and sillimanite are the two orthorhombic and belong to your dipyramidal place team. These discrepa