Aluminium silicate has the chemical formula (AlO)₂SiO₃. It has a density of 2.8 to 2.9 g/cm³, a vitreous lustre, a refractive index of 1.56, a Mohs hardness of 4.5-7.5 (depending upon structure), and can have orthorhombic crystallography. It is insoluble and used as a refractory

Refractory

A refractory material is one that retains its strength at high temperatures. ASTM C71 defines refractories as "non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above...

 in glassmaking

Glass production

Glass production involves two main methods - the float glass process, which produces sheet glass, and glassblowing which produces bottles and other containers.-Glass container factories:...

.

Minerals composed of aluminium silicate include

• Andalusite
  Andalusite
  Andalusite is an aluminium nesosilicate mineral with the chemical formula Al2SiO5.The variety chiastolite commonly contains dark inclusions of carbon or clay which form a checker-board pattern when shown in cross-section....
  
  
• Sillimanite
  Sillimanite
  Sillimanite is an alumino-silicate mineral with the chemical formula Al2SiO5. Sillimanite is named after the American chemist Benjamin Silliman . It was first described in 1824 for an occurrence in Chester, Middlesex County, Connecticut, USA....
  
   (or Bucholzite)
• Kyanite
  Kyanite
  Kyanite, whose name derives from the Greek word kuanos sometimes referred to as "kyanos", meaning deep blue, is a typically blue silicate mineral, commonly found in aluminium-rich metamorphic pegmatites and/or sedimentary rock. Kyanite in metamorphic rocks generally indicates pressures higher than...
  
  

These all have the same chemical composition but are polymorphic

Polymorphism (materials science)

Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...

, having different crystalline structures.

Aluminium silicate is considered to be fireproof for the purposes of building and insulation.