Haüyne - (Na,Ca)_4-8Al₆Si₆(O,S)₂₄(SO₄,Cl)_1-2

Haüyne is a feldspathoid and a member of the sodalite group. It was tentatively named latialite in 1803 by Carlo Giuseppe Gismondi for the locality at Campagna (Latium) without formal publication. Named in 1807 by Toennes Christian Bruun de Neergaard, in honor of abbé Rene Just Haüy ("Father of crystallography"). Named also berzeline in 1831 by Louis Albert Necker de Saussiere, in honor of Joens Jakob Berzelius. The mineral was temporarily named hauynite by James Dwight Dana in 1868.

The sodalite group minerals have a structure based on a cubic structure, which is a tectosilicate framework, of SiO₄ and AlO₄ tetrahedra linked together. The structure is characterized by large cavities, which accommodate large anions (Cl^-, S^2-, SO₄^2-) surrounded by Na+ or Ca+ in tetrahedral coordination. The large anions and cations distinguish minerals of the sodalite group:

• Sodalite Na₈Al₆Si₆O₂₄Cl₂
• Hackmanite Na₈Al₆Si₆O₂₄(Cl,S)₂
• Nosean Na₈Al₆Si₆O₂₄(SO₄)
• Haüyne (Na,Ca)_8-4Al₆Si₆O₂₄(SO₄)_1-2
• Lazurite (Na,Ca)₈Al₆Si₆O₂₄(SO₄,S,Cl)₂

Haüyne occurs in phonolites and related leucite- or nepheline-rich, silica-poor, igneous rocks; less commonly in nepheline-free extrusives and in some metamorphic rocks (i.e marble).

Optical properties:
• Color: Colorless or pale blue.
• Habit: normally forms euhedral dodecahedron crystals yielding hexagonal section. Six, eight and ten-sided cross sections are very common. Rounded corners and corroded, curved and embayed faces are typical.
• Relief: Low, moderate negative.
• Birefringence: Isotropic.
• Special characteristics: Dark rims and exolution inclusions of sub-microscopic Fe-sulphides and Fe-oxides are concentrically arranged ore define linear patterns.

Bibliography

• Cox et al. (1979): The Interpretation of Igneous Rocks, George Allen and Unwin, London.
• Howie, R. A., Zussman, J., & Deer, W. (1992). An introduction to the rock-forming minerals (p. 696). Longman.
• Le Maitre, R. W., Streckeisen, A., Zanettin, B., Le Bas, M. J., Bonin, B., Bateman, P., & Lameyre, J. (2002). Igneous rocks. A classification and glossary of terms, 2. Cambridge University Press.
• Middlemost, E. A. (1986). Magmas and magmatic rocks: an introduction to igneous petrology.
• Shelley, D. (1993). Igneous and metamorphic rocks under the microscope: classification, textures, microstructures and mineral preferred-orientations.
• Vernon, R. H. & Clarke, G. L. (2008): Principles of Metamorphic Petrology. Cambridge University Press.

Photo
Hauyne (with small fluid inclusions) and Sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)	Hauyne (with small fluid inclusions) and Sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)	Hauyne (with small fluid inclusions) and Sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)
Hauyne (with small fluid inclusions) and Sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)	Hauyne (with small fluid inclusions) and Sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)	Hauyne (with small fluid inclusions) and Sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)
Hauyne (with small fluid inclusions) and Sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)	Hauyne (always dark) and Sanidine (I order gray). Laacher See (Germany). XPL image, 2x (Field of view = 7mm)	Hauyne (with small fluid inclusions) and Sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)
Hauyne (with small fluid inclusions) and Sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)	Hauyne (with small fluid inclusions) and Sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)	Hauyne (with small fluid inclusions) and Sanidine (colorless). Laacher See (Germany). PPL image, 2x (Field of view = 7mm)