NOSEAN

    Class : Silicates
    Subclass : Tectosilicates
    Crystal system : Cubic
    Chemistry : Na8Al6Si6O24(SO4) H2O
    Rarity : Rare

Nosean is a rare mineral from the feldspathoid group. Its atomic structure is very close to that of sodalite, the large vacancies being occupied by Na, Cl ions or SO4 groups. It is a mineral of undersaturated rocks, mainly phonolites, much more rarely nepheline syenites. It was named in honor of the German mineralogist Karl Wilhelm Nose who was the first to describe the mineral. Transparent to translucent, nosean is bluish-gray in color, sometimes brown. It rarely occurs in poorly formed to rounded rhombododecahedral crystals but more often in grains or masses (sometimes centimetric) associated with titanite and sanidine (phonolites).

Main photo : Nosean from In den Dellen quarries, Eifel, Germany © Volker Betz

Nosean from Bassano Romano, Italy © Gianfranco Ciccolini
Nosean from Tre Croci, Vico volcanic complex, Italy © Gianfranco Ciccolini
Twinned Nosean from Laacher See Volcanic Complex, Germany © Stephan Wolfsried
Twinned Nosean from In den Dellen quarries, Eifel, Germany © Volker Betz

Nosean in the World

The crystals are generally millimetric and come from Laacher (Eifel, Germany), Somma (Italy), Arucas (Canary Islands, Spain) and the Kola alkaline complex (Russia).

Nosean in France

In France, noséane forms millimetric crystals in the phonolites of the Tuillière and Sanadoire rocks in the Mont-Dore Massif (Puy-de-Dôme), as well as in various phonolitic domes in Cantal.

Twinning

Twins are common on {111}.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 5.5
Density : 2.3 to 2.4
Fracture : Irregular to conchoidal
Streak : White

TP : Translucent to transparent
RI : 1.461 to 1.495
Birefringence : 0
Optical character : None
Pleochroism : None
Fluorescence : Orange

Solubility : Acids

Magnetism : NoneRadioactivity : None

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