Edingtonite |Ba(H2O)4| [Al2Si3O10]
       
Morphology:  
  Tetragonal, 42m or orthorhombic, 222 Single crystals are prismatic up to 10 cm Common forms: {110}, {111}, {111}, and {001}
edingtonite
 
Physical properties:
 

Cleavage:  {110} perfect
Hardness:  4 – 4.5.  D = 2.73 - 2.78 gm/cm3
Luster: vitreous
Streak: white

 
 
Optical properties:
 

Color: Colorless, yellowish to salmon-red; colorless in thin section. Uniaxial ( - or +)
ω  1.480 - 1.506, ε  1.493 - 1.508,  δ 0.002 - 0.013.
Na-rich crystals are length slow, Ca-rich can be length slow or fast
Silky gonnardite prisms on analcime, Verja, Tvedalen, Telemark, Norway. Width of cluster 2 mm. (See Mazzi et al., 1986).

Edingtonite, Ice River, Yoho National Park, British Columbia, Canada. Width of view, 5 mm

 
Crystallography:  
 

Unit cell: a 9.550, b  9.665,  c  6.523 Å
Z = 2.   Space group: P 212121
where disordered:  a  9.584,  c  6.524 Å
Z = 2.   Space Group: P421m

 
     
Name:
 

Edingtonite was described and named by Haidinger (1825) to honor Mr. Edington of Glasgow, in whose collection Haidinger found the first specimen. The type material comes from Kilpatrick Hills, near Glasgow, Scotland. The composition was not known until Heddle (1855) was able to obtain a complete analysis.

     
Crystal structure:
 

Edingtonite is either orthorhombic, space group P 212121 (Taylor and Jackson, 1933; Galli, 1976; Kvick and Smith, 1983; Belitsky et al., 1986) or tetragonal (Mazzi et al., 1984) space group, P421m. Based on optical observations, Akizuki (1986) and Tanaka et al. (2002) also discussed triclinic growth sectors in edingtonite. Orthorhombic edingtonite crystals are (Si,Al) ordered, whereas (Si,Al) disorder increases the symmetry to tetragonal. Kvick and Smith (1983) used neutron diffraction to locate the H positions. edingtonite

The framework of edingtonite consists of the same Al2Si3O10 chains built as natrolite. However, in contrast to natrolite, the tetrahedra are bonded to neighboring chains with no translation parallel to c (see EDI). In the structure drawing here gray tetrahedra represent SiO4 and the green, AlO4. The Ba atoms (red in the figure below) are located in the center of [001] channels on a two-fold axis and are ten-coordinated to six framework oxygens and four H2O molecules (blue). The coordination polyhedra alternate with vacancies parallel to the c-axis similar to the Ca polyhedra in mesolite, scolecite and thomsonite. In the disordered structures Ba may occupy either of two sites (Ba1 and Ba2). Because these sites are about 0.46 Å apart, both cannot be occupied simultaneously. Mazzi et al. (1984) found that the Ba1-site has about 95% occupancy, while Ba2 is about 5%. Ståhl and Hanson (1998) studied the in situ dehydration process using X-ray synchrotron powder-diffraction data and monitored the breakdown of the structure between 660 and 680 K.

     
Chemical composition:
 

Edingtonite shows very little compositional variation, even in the disordered structures. K and Na are commonly present, but do not exceed 0.2 cations per unit cell. However, a possible Ca-dominant edingtonite was found in a sulfide deposit in the Urals, Russia (Ismagilov, 1977). This edingtonite is so intimately intergrown with albite and quartz and is so fine-grained, that it could not be purified for analysis.

     
Occurrences:
 

Edingtonite occurs in epithermal veins of some ore deposits or other alteration systems affecting mafic igneous rocks. Association with such minerals as prehnite indicates temperatures of formation high in the zeolite facies. It also occurs in late stage alteration veins or cavities in nepheline syenite. The following is adapted from Deer et al. (2004).

Hydrothermal alteration and deposition
Edingtonite from the type locality at Old Kilpatrick and nearby quarries west of Glasgow, Scotland, occurs in veins and cavities in Carboniferous andesite. At the Squilver quarry, Shropshire, England, edingtonite is associated with prehnite in alternation veins and breccia in a small dolerite intrusion (Hubbard and Enamy, 1993).

There are several examples of edingtonite occurring in veins of or near epithermal ore deposits. At the Böhlet Manganese Mine, Westergotland, Sweden, edingtonite forms large crystals (to 10 cm) and is associated with manganite (Nordenskjöld, 1895). It occurs in altered basalt near a Zn- and Cu-sulfide epithermal ore deposit at Staré Ransko, eastern Bohemia, Çzech Republic (Novak, 1970). In New Brunswick, Canada, edingtonite occurs in open fractures in Ordovician metamorphic rocks of the Brunswick No. 12 Mine near Bathurst. The mine exploits an epithermal sulfide ore body with quartz, chalcopyrite, galena, pyrite, sphalerite, and barytocalcite (Grice et al., 1984). At Podol’skoye and other pyrite deposits in southern Urals of Russia, calcium edingtonite is intergrown with pyrite in epithermal replacement deposits (Ismagilov, 1977).

The edingtonite in cavities and veins of the Ice River alkaline complex, British Columbia, Canada, is the best example of occurrence in late stage crystallization of nepheline syenite. Here it is associated with natrolite and barite (Grice et al., 1984). At the Jacupiranga Carbonatite Mine, Ribeira de Iguape River Valley southwest of Soa Paulo, Brazil, tiny edingtonite crystals occur on natrolite in vugs in jacupirangite xenoliths in the carbonatite (Menezes and Martin, 1984). Edingtonite is a very rare constituent of miarolitic cavities and veins cutting pegmatite dikes of nepheline syenite at Mont Saint-Hilaire, Quebec, Canada (Horvath and Gault, 1990). Equant crystals of tetragonal edingtonite up to 1 mm occur with barite and carbonate minerals from carbonatite and hydrothermal veins in the Tulilukht Bay area, Khibina massif, Kola Peninsula, Russia (Zaitzev et al., 1992; Khomyakov, 1995).

     
References:
 

Akizuki, M. (1986) Al-Si ordering and twinning in edingtonite. Am. Mineral. 71, 1510-1514.

Belitsky, I.A., Gabuda, S.P., Joswig, W., and Fuess, H. (1986) Study of the structure and dynamics of water in the zeolite edingtonite at low temperature by neutron diffraction and NMR-spectroscopy. Neues Jahrb. Miner. Monatsh. 1986, 541-551.

Deer, A., Howie, R., Wise, W.S., and Zussman, J. (2004). Rock Forming Minerals. vol. 4B. Framework Silicates: Silica Minerals, Feldspathoids and the Zeolites. The Geological Society, London.

Galli, E. (1976) Crystal structure refinement of edingtonite. Acta Crystallogr. 32, 1623-1627.

Grice, J.D., Gault, R.A., and Ansell, H.G. (1984) Edingonite: the first two Canadian occurrences. Can. Mineral. 22, 253-258.

Haidinger, W. (1825) Description of edingtonite, a new mineral species. Edinburgh J. Sci. 3, 316-320.

Heddle, M.F. (1855) Analysis of the mineral “edingtonite”. The London, Edinburgh and Dublin Phil. Mag. and J. Sci. 4th Ser. 9, 179-181.

Horvath, L. and Gault, R.A. (1990) The mineralogy of Mont Saint-Hilaire, Quebec. Mineral. Rec. 21, 284-359.

Hubbard, N. and Enamy, H. (1993) Edingtonite from Squilver Quarry, Shropshire, England. Min. Mag. 57, 349-351.

Ismagilov, M.I. (1977) Calcium edingtonite from pyrite deposits of the southern Urals. Dokl. Acad. Sci. U.S.S.R., Earth Sci. Sect. 234, 170-172.

Khomyakov, A.P. (1995) Mineralogy of hyperagpaitic alkaline rocks. Clarendon Press, Oxford., 223 pp.

Kvick, Å. and Smith, J.V. (1983) A neutron diffraction study of the zeolite edingtonite. J. Chem. Phys. 79, 2356-2362.

Mazzi, F., Galli, E., and Gottardi, G. (1984) Crystal structure refinement of two edingtonites. Neues Jahrb. Miner. Monatsh. 1984, 373-382.

Menezes, L.A.D. and Martins, J.M. (1984) The Jacupiranga Mine, San Paulo, Brazil. Mineral. Rec. 15, 261-270.

Nordenskjöld, O. (1895) Krystallographische und optische untersuchung von Edingtonit. Geol. Foren. Stockholm Forhandl. 17, 597-600.

Novak, F. (1970) Some new data for edingtonite. Acta Univ. Carolinae Geol. 237-251.

Ståhl, K. and Hanson, J.C. (1998) An in situ study of the edingtonite dehydration process from X-ray synchrotron powder diffraction. Eur. J. Mineral. 10, 221-228.

Tanaka, T., Kimura, R., Akizuki, M., and Kudoh, Y. (2002) Origin of low-symmetry growth sectors in edingtonite and yugawarlite, and the crystal structure of the k{011} and v{120} sectors of yugawaralite. Mineral. Mag. 66, 409-420.

Taylor, W.H. and Jackson, W.W. (1933) The structure of edingtonite. Z. Kristallogr. 86, 53-54.

Zaitzev, A.N., Menshikov, Yu.P., and Yakoventchuk, V.N. (1992) Barium zeolites from Khibiny alkaline massif. Zap. Vses. Miner. Ob. 121, 54-61.