Andalusite is an aluminium nesosilicate mineral with the chemical formula Al₂SiO₅.

The variety chiastolite commonly contains dark inclusions of carbon or clay which form an X or a cross in section.

A clear variety first found in Andalusia, Spain can be cut into an interesting gemstone.International Colored Gem Association: Anadalusite Faceted andalusite stones give a play of red, green, and yellow colors that resembles a muted form of iridescence, although the colors are actually the result of unusually strong pleochroism.

Occurrence

---

Andalusite is a common regional metamorphic mineral which forms under high pressure and/or temperature. The minerals kyanite and sillimanite are polymorphs of andalusite, each occurring under different temperature-pressure regimes and are therefore rarely found together in the same rock. Because of this the three minerals are a useful tool to help identify the pressure-temperature paths of the host rock in which they are found.

It was first reported from Andalucia, Spain. in 1789.

Details

---

Crystallographic system	Orthorhombic
Colours	Brown, green, pink, violet and red varieties
Lustre
Hardness	7.5
Specific gravity	3.13 - 3.17
Refractive index	1.641-1.648
cleavage	3
Twinning	Lamellar
Pleochroism	Clear to patchy pink

Related minerals

---

1. Kyanite
2. Sillimanite
3. Chiastolite

References

---

• Mineral galleries
• Webmineral
• Mindat w/ locations

See also

---

• List of minerals

Aluminium minerals | Nesosilicates

Andalusit | Andalucita | Andaluzito | Andalusite | Andalūzitas | Andalúzit | Andalusiet | Andaluzyt | Andaluzita | Andalusit