Akermanite - Encyclopedia

    Class : Silicates
    Subclass : Sorosilicates
    Crystal System : Tetragonal
    Chemistry : CaMgSiO7
    Rarity : Rare

Akermanite is isomorphic to gehlenite, with which it forms a continuous series and whose deposits it often shares. It is the Swedish metallurgist Anders Âkerman who gave it its name. This calcium silicate is a carbonate rock mineral found in basic volcanic rocks rich in calcium, limestone and dolomites transformed by thermal metamorphism, and certain calcic alkaline rocks. Akermanite also crystallizes in abundance in foundry and incinerator furnaces and is therefore an essential constituent of metallurgical slag and incineration bottom ash. It occurs as short prismatic to thin tabular crystals, or in masses ; it is colorless, yellowish-gray, dark green to dark brown. Artificial crystals from foundries and incinerators have acicular to bacillary habits, very different from those of natural crystals. Photo © Stephan Wolfsried - Natural Akermanite from Caspar quarry xenoliths, Bellerberg, Germany

Akermanite in the World

Good crystals of akermanite are known in blocks of metamorphic limestone thrown up by Vesuvius and Somma (Italy), and at Crestmore (California). It is also found in the Oka alkaline complex (Canada) and in several other sites in South Africa and Great Britain.

Akermanite in France

Anthropogenic foundry slags all over the planet frequently contain akermanite crystals - Photo opposite © Pascal Chollet. In France, crystals are found in the slag of Lapanouse-de-Sévérac (Aveyron).


Twin are known on {100} and 001, sometimes cruciform.

Fakes and treatments

No fake reported for this mineral species.

Hardness :  to 6
Density : 2.94
Fracture : Irregular to conchoidal
Trace : White

TP : Translucent to transparent
RI : 1.632 to 1.640
Birefringence : 0.008
Optical character : Uniaxial +
Pleochroism : None
Fluorescence : None

Solubility : Hydrochloric acid

Magnetism : None
Radioactivity : None