HELLANDITE

    Class : Silicates
    Subclass : Sorosilicates
    Crystal system : Monoclinic
    Chemistry : (Ca,Y)6(Al,Fe)B4Si4O20(OH)4
    Rarity : Rare

Hellandite is a complex boron silicate of yttrium and calcium, sometimes metamict. It is essentially a mineral of rare earth granitic pegmatites, in which it notably accompanies allanite, thorite, zircon, thorogummite and phenakite. It was named in honor of the Norwegian geologist Amund Theodor Helland. Hellandite forms prismatic to tabular crystals, exceptionally reaching 30 cm, brown to red-brown and black-brown in color, rarely lighter in color, greenish to cream.

Main photo : Hellandite-(Y) from Lindvikskollen Quarry, Kragerö, Norway © Uwe Haubenreisser

Hellandite-(Y) from Lindvikskollen Quarry, Kragerö, Norway © Oivind Thoresen
Hellandite-(Ce) from Tre Croci, Vico volcanic complex, Italy © Chinellato Matteo
Hellandite from Monte Cavalluccio, Italy © Giuseppe Illuminati
Twinned hellandite-(Y) from Bricco Volti-Monte Ortieul, Piedmont, Italy © Beppe Finello

Hellandite in the World

Hellandite is mainly represented in the Norwegian allanite and titanite pegmatites from Kragerö, and in the American monazite and schorl pegmatites from Riverside County (California). It also forms beautiful crystals in the pegmatite of Wakefield (Quebec). Hellandite is also known in other contexts : granites (Predazzo, Italy), hydrothermalized dolomites rich in rare earths and in the tin-bearing vein of Zaaiplaats, near Potgietersrus (South Africa), in brown-black acicular crystals reaching 10 mm, grouped in tussocks and sprays.

Hellandite in France

In France, hellandite is known in the dolomites of the Trimouns talc deposit near Luzenac (Ariège).

Twinning

Contact and polysynthetic twins are known to be parallel to {001} and {100} and can form crosses.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 4.5 to 6.5
Density : 2.95 to 3.63
Fracture : Undeterminated
Streak : Undeterminated

TP : Translucent
RI : 1.640 to 1.660
Birefringence : 0.020
Optical character : Biaxial +
Pleochroism : None
Fluorescence : None

Solubility : Acids

Magnetism : NoneRadioactivity : Very low

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