Tan acicular crystals of the REE mineral hellandite-(Ce) from a classic locality in Italy: Vetralla, Viterbo Province, Latium. — Photo: David Hospital · CC BY-SA 4.0
Hellandite-(Ce)
Hellandite-(Ce) is an IMA-recognized mineral species in the silicate class, with the chemical formula (Ca,REE)₄Ce₂Al ₂(B₄Si₄O₂₂)(OH)₂.
It crystallizes in the monoclinic crystal system (space group P2/a). It is a member of the Hellandite structural group.
Key properties: [Vitreous to dull.] luster; optically biaxial.
IMA symbol Hld-Ce, IMA status: approved, named in 1999.
Inside miarolitic cavities in alkali-syenite volcanic ejecta in an ignimbrite.
It is found associated with Vonsenite, helvite, baddeleyite, vicanite, britholite.
The name refers to geologist Amund Theodor Helland (1846-1918), of Oslo, Norway. The suffix indicates the dominant REE at the Y site.