Triangular · Square · Hexagonal · Penrose kite–dart · Pan & zoom
A tessellation (or tiling) is a covering of the plane by geometric shapes with no gaps or overlaps. Only three regular polygons tile the plane by themselves: equilateral triangles, squares and regular hexagons. The Penrose tiling, discovered by Roger Penrose in the 1970s, uses two shapes (a "kite" and a "dart" derived from the golden ratio) to create an aperiodic tiling — one that never repeats yet fills the plane completely, exhibiting 5-fold symmetry forbidden in periodic crystals.
In 2023 a single shape called the "einstein" (German for "one stone") was discovered — a 13-sided polygon that tiles the plane aperiodically all by itself, solving a 60-year-old open problem. Penrose tilings appear in nature as quasicrystals, first observed in 1982 by Dan Shechtman (Nobel Prize in Chemistry, 2011). Medieval Islamic architecture at the Darb-i Imam shrine in Isfahan, Iran (1453) contains near-perfect Penrose-like patterns, predating Penrose's work by five centuries.