AENIGMATITE

    Class : Silicates
    Subclass : Inosilicates
    Crystal System : Triclinic
    Chemistry : Na2Fe5TiSi6O20
    Rarity : Rare

Aenigmatite is an infrequent mineral of silica-deficient alkaline igneous rocks. Its name comes from the Greek aenigma (enigma) and reveals the problem initially posed by its chemical composition. It is a velvety black mineral that forms rather coarse elongated prismatic crystals, measuring up to 8 cm, and xenomorphic masses. It is not used in any particular field and remains little known to collectors. 

Main photo : Aenigmatite from Água de Pau Volcano, São Miguel, Azores, Portugal © Luigi Chiappino© Luigi Chiappino

Aenigmatite  in the World

Aenigmatite is notably present in the sodalite syenites of the Ilimaussaq complex, near Narssaq (Greenland), in the alkaline massif of Mont St-Hilaire (Canada), in the nepheline syenites of the Kola peninsula in Russia (Kibiny, Lovozero, Kovdor massifs) and southern Norway (Larvik). It accompanies the usual minerals of alkaline rocks (aegyrine, nepheline, arfvedsonite, etc...).

Aenigmatite in France

Aenigmatite is reported in France in Velay (Haute-Loire) as well as in Rapa Island (French Polynesia).

Twinning

The aenigmatite twins by rotation on (011) or about [010].

Fakes and treatments

No known fakes or treatments.


Hardness : 5.5 to 6
Density : 3
Fracture : Irregular
Trace : Red-brown


TP : Translucent to opaque
RI : 1.780 to 1.900
Birefringence : 0.009 to 0.010
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None

Solubility : Hydrofluoric  acid

Magnetism : Paramagnetic
Radioactivity : None