Hauyne or haüyne, also called hauynite or haüynite (/ɑːˈwiːnaɪt/ ah-WEE-nyte),[7] old name Azure spar,[8]: 571  is a rare tectosilicate sulfate mineral with endmember formula Na3Ca(Si3Al3)O12(SO4).

[4][5] Hauyne was first described in 1807 from samples discovered in Vesuvian lavas in Monte Somma, Italy,[9] and was named in 1807 by Brunn-Neergard for the French crystallographer René Just Haüy (1743–1822).

Since each O is shared between two tetrahedra only half of it "belongs" to the Si ion in either tetrahedron, and if no other components are present then the formula is SiO2, as in quartz.

If the substitution is random the ions are said to be disordered, but in haüyne the Al and Si in the tetrahedral framework are fully ordered.

In haüyne these extra cations are sodium Na+ and calcium Ca2+, and in addition the negatively charged sulfate group (SO4)2− is also present.

[6][13] The refractive index is 1.50; although this is quite low, similar to that of ordinary window glass, it is the largest value for minerals of the sodalite group.

[13] If haüyne is placed on a glass slide and treated with nitric acid HNO3, and then the solution is allowed to evaporate slowly, monoclinic needles of gypsum form.

[4] Associated minerals include nepheline, leucite, titanian andradite, melilite, augite, sanidine, biotite, phlogopite and apatite.