Analcime

Brewsterite series
		Brewsterite-Sr \|(Sr,Ba,Ca)₂(H₂O)₁₀\|[Al₄ Si₁₂ O₃₂] Brewsterite-Ba \|(Ba,Sr)₂(H₂O)₁₀\|[Al₄ Si₁₂ O₃₂]


Morphology:
	Monoclinic 2/m, prismatic crystals with the forms {100}, {010}, {001}, and {011}

Physical properties:
	Cleavage:	{010} perfect, {001} poor
	Hardness:	brewsterite-Sr 5 – 5.5 brewsterite-Ba 4
	D:	brewsterite-Sr 2.45 gm/cm³ brewsterite-Ba 2.50 gm/cm³
	Luster:	vitreous
	Steak:	white
			Brewsterite-Sr, Whitesmith Mine, Strontian, Ardnamurchan Highland Region, Scotland. Image width 8 mm. © Volker Betz
Optical properties:
	Color:	Colorless, white, yellowish, grey, greenish; colorless in thin section
	Brewsterite-Sr:	biaxial (+), a 1.510, b 1.512, g 1.523, d .013, 2Vz 65° Z = b, X ˄ c = 19° - 34°
	Brewsterite-Ba:	biaxial (+) a 1.513, b 1.517, g 1.527, d .014, 2Vz 57° Z = b, X ˄ c = 36°
Crystallography:
	Unit cell:
	brewsterite-Sr	a 6.793, b 17.573, c 7.759 Å, b 94.54°. Z = 1, Space group P21/m or P21 or commonly: a 6.782, b 17.510, c 7.740, α 89.90°, β 94.09°, γ 90.10°, space group P1
	brewsterite-Ba	a 6.780, b 17.599, c 7.733 Å, β 94.47°Z = 1, Space group P21/m or P21

Name:
	Brewsterite was described and named by Brooke (1822) to honor Sir David Brewster (1781-1868), Scottish mineralogist and natural philosopher, who formulated the optical behavior of light in anisotropic crystals. The type material comes from the galena-bearing veins at Strontian, Argyll, Scotland. Coombs et al. (1997) have elevated the name to series status to include two species. Brewsterite-Sr is the new name for the original material, in which Sr is the most abundant non-framework cation. Brewsterite-Ba is a new species with the type example from the Gouverneur Talc Company’s No. 4 wollastonite mine near Harrisville, Lewis County, New York, U.S.A. (Robinson and Grice 1993).

Crystal structure:
	Brewsterite is one of the tabular zeolites, a group including stilbite and heulandite, which have a prominent {010} cleavage. The structure of brewsterite was determined and refined by Perrotta and Smith (1964) and later refined by Schlenker et al. (1977), Artioli et al, (1985), and Cabella et al. (1993) all finding the space group P21/m. As in all tabular zeolites, there are two sets of interconnecting channels in the framework (see BRE). Eight-membered rings (aperture 2.3 x 5.0 Å) form channels parallel to a-axis, and second set of eight-membered rings (aperture 2.8 x 4.1 Å) forms channels parallel to the c-axis. Schlenker et al. (1977) showed that the framework in the crystal they refined is partially ordered. Almost no Al occurs in D tetrahedral site (light gray tetrahedra), but is approximately evenly distributed between the A, B, and C sites (darker gray tetrahedra), labeled in the lower right corner. Neutron diffraction data by Artioli et al. (1985) confirmed this partial ordering. Each Sr (or Ba) is bonded to four framework oxygens and five H2O molecules (see the 8-ring channel on the right side of the drawing). Cabella et al. (1993) found that about 92% of Ba occupies the same site as the Sr, but there are two other alternate sites slightly displaced from the Ba1 site, remaining on the mirror plane. Artioli et al. (1985) with neutron diffraction data from a sample of brewsterite from Yellow Lake, British Columbia, showed that the hydrogen atoms for the W4 H2O molecule have three possible orientations. Two of these cause the mirror plane to disappear, lowering the symmetry to P21. It has been known since the observations of Des Cloizeau (1874) that (010) cleavage sections are divided into three sectors based on extinction angles. These are growth sectors from the {010}, {011}, and {610} faces (Akizuki 1987). Akizuki et al. (1996) show that in a sample from Strontian, Scotland, each sector has a slightly different composition, in both Si/Al and Ba/Sr. Furthermore, each has slightly different Al occupancies in framework tetrahedral sites. Both the {011} and {610} sectors have sufficiently different occupancies between A and A’, B and B’, and C and C’ that they have triclinic symmetry. The occupancies in the {010} sector are very nearly the same across the mirror planes, maintaining monoclinic symmetry.All structure refinements located only one fully occupied channel-cation position. This site is located in the middle of the [100] channels and is nine-coordinated to four framework oxygens and five channel H2O molecules. Artioli et al. (1985) also located the H positions in the channels based on neutron diffraction data. Upon dehydration up to 684 K, brewsterite loses eight of its ten H2O molecules accompanied by diffusion of the channel cations and framework distortion (Ståhl and Hanson 1999). In a dehydration experiment with 24-h equilibration in vacuum at 550 K, Alberti et al. (1999) observed statistical breaking of T-O-T bonds and formation of an altered tetrahedral topology.


Chemical composition:

With few natural examples, and even fewer analyses, little compositional variation is known. It is clear that the principal variation is in the exchangeable cations Sr and Ba. All samples contain minor Ca, while Na, K, and Mg are even less common. The Si content of the framework is nearly constant with TSi varying from 0.73 to 0.75. The H₂O content is typically 10 molecules per unit cell, which corresponds to about 13.7 weight per cent H2O in the analysis

Occurrences:
	Both brewsterite-Sr and brewsterite-Ba occur in environments affected by hydrothermal fluids, either with epithermal ore deposits or late stage alteration related to metamorphic events. The rarity of these minerals is mostly a result of chemical control rather than physical stability. Brewsterite-Sr was first found in the lead mines at Strontian, Argyll, Scotland. It occurs in epithermal veins, containing galena in a gangue assemblage of calcite, barite, harmotome, brewsterite-Sr. The veins occur along the vertical contact between the Moine schist and Strontian granite (Tschnerich 1992). Brewsterite-Sr occurs in several localities in metamorphosed rocks in France, such as at St. Cristophes near Borg d’Oisans, Department de l’Isere. Excellent crystals have been found in a limestone quarry in the Riou Maou Mountains between Gavarie and Luz near the Saint-Sauveur River, Bareges, in the high Pyrenees. Here it is associated with calcite, chabazite, and laumontite. Khomyakov et al. (1970) describe brewsterite-Sr from joints and cavities in aplite and syenite in the Burpala Pluton, North Baikal Region, Siberia, Russia. The brewsterite-Sr is associated with stilbite, heulandite, natrolite, and pyrite. Brewsterite-Sr occurs in veins cutting vesicular trachyte along north side of Yellow Lake and in cliffs near Twin Lakes near Olalla in southern British Columbia, Canada (Tschnerich 1992, p. 83), where it is associated with calcite, fluorite, and heulandite. Brewsterite-Ba was first found at the Gouverneur Talc Company’s No. 4 open-pit wollastonite mine on New York Route 3 southeast of Bonaparte near Harrisville, Lewis County, New York. It occurs in cavities in prehnite, associated with prehnite, quartz, diopside, calcite, wollastonite, and microcline. The assemblage appears to post-date wollastonite and probably formed from late stage hydrothermal fluids. At the Cerchiara mine, La Spezia, Liguria, Italy, brewsterite-Ba occurs in the schistose layer above radiolarian chert, where it is associated with Mg-rich, phengitic mica and chlorite. It also occurs in fractures in the fold hinges in radiolarian chert beds, associated with pectolite, Ba-Ca carbonate, and barite (Cabella et al. 1993).
References:
	Akizuki, M. 1987. Crystal symmetry and order-disorder structure of brewsterite. Am. Mineral. 70, 822-828. Akizuki, M., Kudoh, Y. and Kuribayashi, T. 1996. Crystal structures of the {011}, {610}, and {010} growth sectors in brewsterite. Am. Mineral. 81, 1501-1506. Alberti, A., Sacerdoti, M., Quartieri, S., and Vezzalini, G. 1999. Heating-induced phase transformation in zeolite brewsterite: new 4- and 5-coordinated (Si,Al) sites. Phys. Chem. Minerals 26, 181-186. Artioli, G., Smith, J.V. and Kvick, Å. 1985. Multiple hydrogen positions in the zeolite brewsterite (Sr0.95,Ba0.05)Al2Si6O16•5H2O. Acta Crystallogr. C41, 492-497. Brooke, H.J. 1822. On the comptonite of Vesuvius, the brewsterite of Scotland, the stilbite and the heulandite. Edinburgh Philos. J. 6, 112-115. Cabella, R., Lucchetti, G., Palenzona, A., Quartieri, S. and Vezzalini, G. 1993. First occurrence of a Ba-dominant brewsterite: structural features. Eur. J. Mineral. 5, 353-360. 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. De Cloizeau, A. 1874. Manual de mineralogie, p. 420-422. Dunod, Editeur, Paris. Khomyakov, A.P., Katayeva, Z.T., Kurova, T.A. and Rudnitskaya, Y.S. and Smol’yaninova, N.N. 1970. First find of brewsterite in the USSR. Doklady Akad Nauk SSSR, 190, 146-149. Perrotta, A.J. and Smith, J.V. 1964. The crystal structure of brewsterite, (Sr,Ba,Ca)2(Al4Si12O32)•10H2O. Acta Crystallogr. 17, 857-862. Robinson, G.W. and Grice, J.D. 1993. The barium analog of brewsterite from Harrisville, New York. Can. Mineral. 31, 687-690. Schlenker, J.L., Pluth, J.J. and Smith, J.V. 1977. Refinement of the crystal structure of brewsterite, Ba0.5Sr1.5Al4Si12O32•10H2O Acta Crystallogr. B33, 2907-2910. Ståhl, K. and Hanson, J.C. 1999. Multiple cation sites in dehydrated brewsterite. An in situ synchrotron powder diffraction study. Microporous Mesoporous Materials 32, 147-158. Tschernich, R.W. (1992) Zeolites of the World, Geoscience Press, Phoenix, Arizona. 563 pp.