Chiavennite |CaMn(H2O)2| [Be2Si5O13(OH)2]
Ferrochiavennite |Ca1-2Fe(H2O)2| [Be2Si5O13(OH)2]
       
Morphology:    
  Spherical aggregates of platy, spear-shaped crystals. Twinning on {100} is common.
   
Physical properties:  
  Cleavage: {100}, {010}, and {001} good to perfect.
Hardness:  ~3.
D (chiavennite) = 2.56 - 2.64 g/cm3.
D (ferrochiavennite) = 2.67 g/cm3.
Luster: Vitreous to pearly.
Streak: White to pale ocher.
          Chiavennite
 
Optical properties:
 

Color: Pale orange-yellow, colorless  to yellow or orange-yellow in thin section.
Biaxial (+).
Chiavennite: α 1.594 - 1.596, β 1.600, γ 1.613 - 1.618, δ 0.008, 2Vz (calc) = 50°.  Dispersion: r < v.
 X = a, Y = b, Z = c. 
Ferrochiavennite: α 1.583(1), β 1.589, γ 1.602, 2Vz (meas) = 62°. 
 X ~ a, Y ~ b, Z ~ c. 
Pleochroism: X = colorless to pale yellow, Z = yellow-orange. Absorption: Z > X.
 
Crystallography:
 

Unit cell data:

Chiavennite
a  8.747,  b  4.897,  c  31.316 Å.
Z = 4 ,  Space group P21/c.  (Cametti and Armbruster 1995)

Ferrochiavennite
a  8.759,  b  4.684,  c  31.258 Å.
Z = 4 ,  Space group P21/c. (Grice et al. 2013)

 
 
     
Name:  
 

Chiavennite was described and named by Bondi et al. (1983) for the locality at Tanno, Chiavenna, Rhetic Alps of Italy. The mineral was later classified as a zeolite by Coombs et al. (1997). It is a rare mineral occurring in two known localities in Italy and the Oslo area of Norway, although more recently a boron-bearing chiavennite has been reported from Utö, Stockholm, Sweden (Langhof and Holstram, 1994).
Ferrochiavennite was described by Grice et al. (2013) based on material from two syenite pegmatite localites in Norway: Blåfjell, Langangen, Telemark, and the AS Granit larvikite quarry, Tveladen, Vestfold.
       
Crystal structure:  
  The structure of Chiavennite was originally described in the non-centrosymmetric space group P21ab (Domeneghetti et al. 1981). However, further X-ray analysis suggested the centrosymmetric space group Pnab (Tazzoli et al. 1995). New data indicate that, in spite of the pseudo-orthorhombic cell dimension, chiavennite is truly monoclinic P21/c (b ? 90) and twinned as recently shown for the new mineral ferrochiavennite (Cametti and Armbruster 2015). The structure of both chiavennite and ferrochiavennite consists of an interrupted framework of SiO4 and BeO4 tetrahedra (Tazzoli et al. 1995). Be and one Si tetrahedral site (Si1) form a chain of singly connected 4-rings parallel to the a-axis (see figure). The Be tetrahedra link to zigzag chains of Si3 tetrahedra, which in turn are linked to another zigzag chain of Si2 tetrahedra. Both zigzag chains are parallel to the c-axis (-CHI). The Be tetrahedra each have a hydroxyl on one apex. The framework contains nine-ring channels parallel to the c-axis.
Ca cations (orange) and H2O molecules (blue) are located within the nine-ring channels, where each cation is coordinated with four framework oxygens, two hydroxyls, and two H2O molecules. Mn cations (red) are located between Be-Si1 4-ring chains, where they are coordinated with four framework oxygens and two hydroxyls. The chemical analyses suggest that some Al may be substituting for Si. The Si1-O bond lengths average 1.627, indicating that the Si1 site may be the one containing the Al. (The Si-O bond length for tetrahedra with no Al is commonly about 1.605) Upon dehydration, continuous monoclinic–orthorhombic transition from space group P21/c to Pbcn is attributed to destruction of hydrogen bonds between extraframework H2O as donor and oxygen at the cavity walls as acceptor (Cametti and Armbruster 2015).
  Chiavennite
   
Chemical composition:
  Analyses of chiavennite are available from two localities, Chiavenna, Italy (Bondi et al., 1983) and Longangen, Norway (Raade et al., 1983). If the cell contents are calculated by the method used for other zeolites, the results give a large +E%. A positive error indicates too many cations are assigned to the framework, such as the Al, or some non-framework cations are missing.
   
Occurrences:
 

Chiavennite occurs in altered alpine pegmatite dikes cutting the Chiavenna mafic and ultramafic complex in the Rhetic Alps of Italy. Crusts of chiavennite and bavenite on pre-existing beryl indicate late stage reaction with pegmatitic fluids. Bondi et al. (1983) suggest that the Be came from beryl, of course, but Ca and Mn may have been derived from the mafic and ultramafic wall rocks.

Chiavennite occurs in syenite pegmatite dikes at many localities in the Oslo region of Norway. The original discovery area is the Heia quarry, Tvedalen, 10 km west of Larvik, and other areas are a road exposure at Blåfjell, Langangen; at Bakkane, Brunlanes about 3 km SW of Larvik; and Vevja (Bakken) quarry also in the Tvedalen district. At each locality chiavennite is the latest phase in vugs or druses, associated with natrolite and analcime. Other Be minerals in the pegmatite dikes, not necessarily in the same vugs as chiavennite, include eudidymite, helvite, leucophanite, gadolinite-(Ce), and hamburgite (Raade et al., 1983). Chiavennite in these dikes is a late stage phase growing from fluids, rather than a reaction product (see Pezzotta et al., 2004, for a complete listing of localities).

Ferrochiavennite is described by Grice et al. (2013) from two syenite pegmatite localites in Norway: Blåfjell, Langangen, Telemark, and the AS Granit larvikite quarry, Tveladen, Vestfold.

Exceptional chiavennite crystal groups up to 2mm have been found associated with pezzottaite in the Sakavalana pegmatite at Ambatovita, in central-western Madagascar (Pezzotta et al., 2004). The chiavennite formed as a late stage mineral together with hambergite, a late generation of pezzottaite, and some masses of Mn-hydroxides (mainly cryptomelane).
   
References:
 

Bondi, M., Griffin, W.L., Mattioli, V., and Mottana, A. (1983) Chiavennite, CaMnBe2Si5O13(OH)2?2H2O, a new mineral from Chiavenna (Italy). Am. Mineral. 68, 623-627.

Cametti, G. and Armbuster, T. (2015) Chiavennite revisited: a high-temperature in situ single-crystal X-ray diffraction study. Eur. J. Mineral. 27, 659-667.

Coombs, D.S., Alberti, A., Armbruster, T., Artioli, G., Colella, C., Galli, E., Grice, J.D., Liebau, F., Mandarino, J.A., Minato, H., Nickel, E.H., Passaglia, E., Peacor, D.R., Quartieri, S., Rinaldi, R., Ross, M., Sheppard, R.A., Tillmanns, E., and Vezzalini, G. (1997) Recommended nomenclature for zeolite minerals: Report of the Subcommittee on Zeolites of the International Mineralogical Association, Commission on New Minerals and Mineral Names. Can. Mineral. 35, 1571-1606.

Domeneghetti, M.C., Rossi, G., and Tazzoli, V. (1981) La struttura cristallina di un nuovo silicato manganesifero delle pegmatiti di Chiavenna. Rend. Soc. It. Min. Petr. 37, 994.

Grice, J.D., Friis, H. and Kristiansen, R. (2016) New Data For Chiavennite and Ferrochiavennite. Can. Mineral., 54, 21-32.

Grice, J.D. Kristansen, R., Friis, H., Rowe, R., Poirier, G.G., Selbekk., R.S., Cooper, M.A., and Larsen, O.A. (2013) Ferrochiavennite, a new beryllium silicate zeolite from syenite pegmatites in the Larvyk pluton complex, Oslo region, southern Norway. Can. Mineral. 51, 285-296.

Langhof, J. and Holstram, D. (1994) Boron-bearing chiavennite and other late stage minerals of the proterozoic lithium-pegmatites of Utö, Stockholm, Sweden. IMA, 16th General Meeting (4-9 September, Pisa, Italy), Abstracts, 232.

Pezzotta F., Guastoni A., Forner H., Demartin F., Kristiansen R. (2004) Exceptional chiavennite associated with pezzottaite from the Sakavalana Pegmatite, Ambatovita, Madagascar. Pegmatite Interest Group web site of Mineralogical Society of America. www.minsocam.org/msa/Pegmatites.html

Raade, G., Åmli, R., Mladeck, M.H., Din, V.K., Larsen, A.O., and Åsheim, A. (1983) Chiavennite from syenite pegmatites in the Oslo region, Norway. Am. Mineral. 68, 628-633.

Tazzoli, V., Domeneghetti, M.C., Mazzi, F., and Cannillo, E. (1995) The crystal structure of chiavennite. Eur. J. Mineral. 7, 1339-1344.

Updated: April 2025.