# Haüyne

- Page: https://taslar.bumba.tr/en/stones/hauyne/
- Turkish: Hauyn
- Also known as: Hauyne, Hauynite
- Kind: Mineral
- Classification: Minerals › Silicates › Tectosilicates
- Chemical formula: (Na,Ca)₄₋₈Al₆Si₆(O,S)₂₄(SO₄,Cl)₁₋₂
- Crystal system: Cubic
- Hardness (Mohs): 5.5–6
- Specific gravity: 2.44–2.5 g/cm³
- Refractive index: 1.494–1.509
- Lustre: Vitreous (glassy), Greasy
- Transparency: Transparent, Translucent
- Colours: bright blue, greenish blue, white, grey, black, brown, green, yellow, red
- Streak: Very pale blue to white
- Cleavage: Distinct on {110}
- Fracture: Uneven to conchoidal; brittle
- Value ladder: 4/9 step, Fine dimension stone and ore
- Last checked: 2026-10-04

Small, vivid blue grains glittering in volcanic rock: a gemstone rarely seen in cut form.

Haüyne is a sodalite-group mineral made of sodium, calcium, aluminium, silicon, oxygen and sulfate. Its best-known colour is bright blue; it can also be white, grey, green or reddish. It occurs as small grains or crystals in silica-poor volcanic rocks such as phonolite. It was first described in 1807 from Vesuvian lavas of Monte Somma in Italy and named after the French crystallographer René Just Haüy. It is sometimes cut as a gemstone, but cut haüyne is very rare.

## How does it form?

Haüyne forms in silica-poor volcanic rocks rich in leucite or nepheline, such as phonolite; less commonly it occurs in volcanic rocks without nepheline. It grows as small grains or crystals within the rock as the magma cools. That is why it occurs with nepheline, leucite, melilite, augite, sanidine, biotite and apatite. It is a member of the sodalite group, which also includes sodalite, nosean and lazurite.

According to the Handbook of Mineralogy, its best-known localities are the Alban Hills near Rome (Ariccia, Marino), Monte Somma and Monte Vulture in Italy, and the Mendig and Mayen area of the Eifel in Germany.

## What is it used for?

- **Gemstone:** Its bright blue, transparent pieces are sometimes cut as gemstones; cut stones are rare and small.
- **Collecting:** Its vivid blue crystals in volcanic rock are sought by collectors.

## How to recognise it

- Bright blue or greenish-blue small grains or crystals with a vitreous to greasy lustre.
- Its crystals are dodecahedra or octahedron-like shapes and rarely exceed 3 cm.
- Hardness 5.5–6; a steel knife scratches it only with difficulty.
- Usually found in volcanic rocks such as phonolite, with nepheline, leucite and sanidine.
- Some specimens glow reddish orange to purplish pink under long-wave ultraviolet light.

## Fakes and imitations

- Sodalite and lazurite are blue minerals of the same group, but they are usually found as masses. Haüyne mostly occurs as small, bright blue grains or crystals within volcanic rock. A certain distinction is made in the laboratory.
- Cut blue haüyne can be mistaken for sapphire or other blue stones; haüyne is much softer (Mohs 5.5–6) and has a lower refractive index (about 1.50).

## What determines its value?

Haüyne is a rare gemstone whose value depends on the vividness of its colour, its transparency and its size. Cut stones are usually very small, and bright, saturated blue ones are sought by collectors. In rough form, specimens with bright blue crystals in volcanic rock are also valued in collections.

This information is educational, not buying, selling or investment advice. Value varies enormously with quality and treatment.

## Myths and misconceptions

- Myth: Blue haüyne is a kind of sapphire. Fact: Haüyne is a sodalite-group silicate mineral unrelated to sapphire. Sapphire is corundum and much harder (Mohs 9); haüyne has a hardness of 5.5–6.

## Curious questions

**Why is haüyne rarely seen as a gemstone?**

Its crystals are generally small and occur as single grains within volcanic rocks. Pieces transparent and large enough to cut are scarce, and with a hardness of 5.5–6 it is relatively soft. Cut haüyne is therefore rare and mostly found in collections.

## Did you know?

- It is named after René Just Haüy, regarded as one of the founders of crystallography.
- Its crystals are generally small, growing up to 3 cm, which is why cut haüyne gems are usually tiny.
- The Laacher See volcanic area in Germany's Eifel region is known for attractive, gem-quality blue haüyne.

## Where is it found?

- Monte Somma (Vesuvius), Campania, Italy (Type locality): Haüyne was first described in 1807 from samples found in the Vesuvian lavas of Monte Somma
- Laacher See, Eifel, Rhineland-Palatinate, Germany (Major deposit): The Laacher See volcanic area yields attractive blue gem specimens; the Mendig and Mayen area is also known
- Alban Hills (Colli Albani), Lazio, Italy (Known locality): Haüyne occurs at many places here, such as Ariccia and Marino

## Sources

- [Haüyne](https://en.wikipedia.org/wiki/Ha%C3%BCyne), Wikipedia
- [Handbook of Mineralogy: Haüyne](https://www.handbookofmineralogy.org/pdfs/hauyne.pdf), Mineralogical Society of America


Source: https://taslar.bumba.tr/en/stones/hauyne/ · Licence: CC BY-SA 4.0