Orange brown crystals of the rare mineral chiavennite associated to tetragonal colorless natrolite crystals from Vevja Quarry, Tvedalen, Larvik, Vestfold, Norway. — Photo: David Hospital · CC BY-SA 4.0
Chiavennite
Chiavennite is an IMA-recognized mineral species in the silicate class, with the chemical formula CaMn²⁺(BeOH)₂Si₅O₁₃·2H₂O.
It crystallizes in the orthorhombic crystal system (space group Pnab).
Key properties: Mohs hardness 3; specific gravity 2.56–2.64; White to pale ocher streak; Vitreous to pearly luster; optically biaxial.
IMA symbol Cve, IMA status: approved, named in 1981.
Coating beryl in late-stage pegmatites (Tanno, Italy); in vugs in syenite pegmatites (Norway).
It is found associated with Beryl, bavenite (Tanno, Italy); analcime, aegirine, helvite, eudidymite, natrolite, feldspar (Norway).
The name refers to the Italian locality at Tanno, Chiavenna.