Haüyne

Haüyne is a rare tectosilicate mineral within the feldspathoid group, with the chemical formula (Na,Ca)₄-₈Al₆Si₆(O,S)₂₄(SO₄,Cl)₁-₂. It is characterized by its distinctive blue color, which can range from pale to intense azure. The name haüyne honors the French mineralogist Abbé René Just Haüy.

This mineral typically forms in silica-poor, alkali-rich igneous rocks, such as nepheline syenites and phonolites. It often occurs as small, euhedral to subhedral crystals, commonly found as inclusions in larger mineral grains. Haüyne can also be found in volcanic ashes and ejecta.

A notable feature of haüyne is its tendency to fluoresce under ultraviolet light, often exhibiting a yellow or orange glow. It is moderately hard, with a Mohs hardness of 5.5 to 6, and has a vitreous luster. The presence of sulfate or chloride ions within its structure is a defining characteristic, distinguishing it from other feldspathoids.

Haüyne is not a commercially significant mineral but is of interest to mineral collectors and geologists due to its unusual composition and occurrence. Large, well-formed crystals are rare and highly prized. Its presence in volcanic rocks can provide clues about the magmatic conditions under which they formed.