Hellandite - Encyclopedia
Class : Silicates
Subclass : Sorosilicates
Crystal system : Tetragonal
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 in the World
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