Hauyne

Haüyne
Haüyne on augite, Somma-Vesuvius Complex, Naples Province Italy
General
Category	Tectosilicate, sodalite group
Formula (repeating unit)	Na₃Ca(Si₃Al₃)O₁₂(SO₄)
Strunz classification	9.FB.10 (10 ed) 8/J.11-30 (8 ed)
Dana classification	76.2.3.3
Crystal system	Isometric
Crystal class	Hextetrahedral (43m) H-M symbol (4 3m)
Space group	P43n
Unit cell	a = 9.08 - 9.13 Å; Z = 2
Identification
Formula mass	1,032.43 g/mol
Color	Blue, white, gray, yellow, green, pink
Crystal habit	Dodecahedral or pseudo-octahedral
Twinning	Common on {111}
Cleavage	Distinct on {110}
Fracture	Uneven to conchoidal
Tenacity	Brittle
Mohs scale hardness	5 to 6
Luster	Vitreous to greasy
Streak	Very pale blue to white
Diaphaneity	Transparent to translucent
Specific gravity	2.4 to 2.5
Optical properties	Isotropic
Refractive index	n = 1.494 to 1.509
Birefringence	None, isotropic
Pleochroism	None, isotropic
Fusibility	4.5
Solubility	Gelatinises in acids
Other characteristics	May fluoresce orange to pink under longwave ultraviolet light
References

Hauyne, haüyne (pronunciation: /ɑːˈwin/), hauynite or haüynite is a tectosilicate mineral with sulfate, with endmember formula Na₃Ca(Si₃Al₃)O₁₂(SO₄). As much as 5 wt % K₂O may be present, and also H₂O and Cl. It is a feldspathoid and a member of the sodalite group. Hauyne was first described in 1807 from samples discovered in Vesuvian lavas in Monte Somma, Italy, and was named in 1807 by Brunn-Neergard for the French crystallographer René Just Haüy (1743–1822). It is sometimes used as a gemstone.

Formulae:

All these minerals are feldspathoids. Haüyne forms a solid solution with nosean and with sodalite. Complete solid solution exists between synthetic nosean and haüyne at 600 °C, but only limited solid solution occurs in the sodalite-nosean and sodalite-haüyne systems.

Haüyne belongs to the hexatetrahedral class of the isometric system, 43m, space group P43n. It has one formula unit per unit cell (Z = 1), which is a cube with side length of 9 Å. More accurate measurements are as follows:

All silicates have a basic structural unit that is a tetrahedron with an oxygen ion O at each apex, and a silicon ion Si in the middle, forming (SiO₄)⁴⁻. In tectosilicates (framework silicates) each oxygen ion is shared between two tetrahedra, linking all the tetrahedra together to form a framework. 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.

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