HASTINGSITE

    Class : Silicates
    Subclass : Inosilicates
    Crystal system : Monoclinic
    Chemistry : NaCa2Fe5(Si6Al2)O22(OH)2
    Rarity : Rare

Hastingsite is a sodium, calcium and iron amphibole, formerly considered a variety of "hornblende". It is now recognized as a mineral in its own right and forms a continuous series with magnesio-hastingsite, its magnesium equivalent. It is present in nepheline syenites, orthogneisses and amphibolites, as well as in certain skarns. It owes its name to its location of discovery : Hastings County (Ontario, Canada). Hastingsite forms elongated or stocky prismatic crystals with a hexagonal section, rarely doubly-terminated, with frequently rounded edges. Hastingsite is also known in more or less fibrous to bacillary masses or aggregates, sometimes grainy. The color is usually black-brown, sometimes brown.


Main photo : Hastingstite from St Christoph Mine, Saxony, Germany © Uwe Haubenreisser

Hastingstite from Franklin Mine, New Jersey, USA © Christopher O'Neill
Hastingstite from Monte de São Bartolomeu, Leiria, Portugal © Rui Nunes
Hastingstite from Kara Mines, Tasmania, Australia © Andrew Tuma
Hastingstite from Sampo mine, Shitouyouze, Okayama, Japan © Jeff Weissman

Hastingstite in the World

The localities providing the most beautiful hastingsite crystals are Bancroft (Canada), Franklin (New Jersey) with chunky crystals of 4 cm, the island of Los (Republic of Guinea) where the small shiny black crystals exceed 1 cm. It is also found in Uppsala (Sweden) in nepheline syenites.

Hastingstite in France

In France, hastingsite is known at the Madec quarry (Côtes d'Armor), in the nepheline syenite of Fitou, near Narbonne (Aude) and at Feilluns and in the Canigou Massif (Pyrénées-Orientales).

Twinning

Twins are single or multiple and parallel to {100}.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 5 to 6
Density : 3.35 to 3.5
Fracture : Irregular
Streak : Grey-green

TP : Translucent
RI : 1.669 to 1.705
Birefringence : 0.015 to 0.025
Optical character : Biaxial -
Pleochroism : Visible
Fluorescence : None

Solubility : Insoluble

Magnetism : NoneRadioactivity : None