Light beige crystal aggregates of the rare Ca-Be silicate mineral tvedalite from the type locality in Tvedal, Norway (Vevja Quarry, Tvedalen, Larvik, Vestfold og Telemark, Norway). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY 4.0
Tvedalite
Tvedalite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ca₄Be₃Si₆O₁₇(OH)₄·3H₂O.
It crystallizes in the orthorhombic crystal system.
Key properties: Mohs hardness 4.5; specific gravity 2.541; White streak; Vitreous luster.
IMA symbol Tve, IMA status: approved, named in 1990.
Found in nepheline syenite pegmatite.
It is found associated with Chiavennite, analcime, natrolite, parisite-(Ce), bastnÄasite-(Ce), leucophanite, epididymite, albite, calcite, chlorite, todorokite, fluorite, magnetite.
The name refers to the Tvedalen area in Norway, which has produced many interesting minerals from the nepheline syenites.