title: Holmium–magnesium–zinc quasicrystal
text: # Holmium–magnesium–zinc quasicrystal
  
  A holmium–magnesium–zinc (Ho–Mg–Zn) quasicrystal is a quasicrystal made of an alloy of the three metals holmium, magnesium and zinc that has the shape of a regular dodecahedron, a Platonic solid with 12 five-sided faces. Unlike the similar pyritohedron shape of some cubic-system crystals such as pyrite, this quasicrystal has faces that are true regular pentagons.
  
  The crystal is part of the R–Mg–Zn family of crystals, where R=Y, Gd, Tb, Dy, Ho or Er. They were first discovered in 1994. These form quasicrystals in the stoichiometry around R $_9Mg$ $_{34}Zn$ $_{57}.$ Magnetically, they form a spin glass at cryogenic temperatures.
  
  While the experimental discovery of quasicrystals dates back to the 1980s, the relatively large, single grain nature of some Ho–Mg–Zn quasicrystals has made them a popular way to illustrate the concept.
  
  