Cowlesite


Gismondine		\|Ca₄ (H₂O)₁₈\| [Al₈Si₈O₃₂]

Morphology:
	Crystals are bipyramidal, composite to 2 cm. In stellate or radiating aggregates. Ubiquitous twinning on the normal to {100} giving pseudotetragonal individuals.

Physical properties:
	Cleavage: {232 } distinct. Fracture: uneven to subconchoidal. Hardness: 4.5. D = 2.20 to 2.26 gm/cm³. Luster: vitreous. Streak: white.

Optical properties:
	Color: colorless to grayish; colorless in thin section. Biaxial (-). α = 1.525 - 1.540, β = 1.531 - 1.544, γ = 1.541 - 1.550, δ= 0.010 - 0.016, 2V_x = 82 - 86°. Z ˄ c = 42°, Y = b, O.A.P. ^ (010).		Optic orientations in twinned gismondine

Crystallography:
	Unit cell data: a 10.023, b 10.616, c 9.843 Å, β 92.42°. Z = 1, Space group P2₁/c. (Rinaldi and Vezzalini 1985).



Name:
	Gismondine was named by von Leonhard (1817) named after Carlo Giuseppe Gismondi (1762-1824), lecturer in mineralogy in Rome. Gismondi (1817) had discovered the material at Capo di Bove, near Rome, Italy, naming it zeagonite, which was not accepted as a new mineral, because his sample was a mixture of gismondine and phillipsite.

Crystal structure:
	The gismondine framework topology consists of two sets of intersecting, doubly connected 4-membered rings linked into double crankshaft chains (dcc on the GIS page), like those of phillipsite. These sets of double crankshaft chains that run parallel to the a-axis and to the b-axis are related by a 4₁ axis forming the GIS framework. Where there is (Si,Al) disorder in the tetrahredra, the topological symmetry is I4₁/amd. However, in gismondine ordering of the framework and restrictions caused by distribution of channel cations and H₂O molecules lower the symmetry to P2₁/c.
	Through this framework, channels confined by eight-membered rings (aperture 3.0 x 4.7 Å) are parallel to the a- and b-axes. The Ca site (red) is displaced from the center of the cavity at the intersection of the eight-membered ring channels and is attached to one side of the eight-membered ring (see the accompanying figure). Ca is coordinated to two framework oxygens and four H₂O molecules (Fischer and Schramm 1971), Rinaldi and Vezzalini 1985). Artioli et al. (1986) located all proton positions by single-crystal neutron diffraction at 15 K and found two statistically distributed configurations for the Ca coordination. In the more common configuration (70%), Ca is six-coordinated. In the other variant (30%), one H₂O molecule splits to new sites (light blue circles); thus, the coordination becomes seven-fold. Upon partial dehydration gismondine undergoes several phase transitions accompanied by symmetry reduction (van Reeuwijk 1971, Vezzalini et al. 1993, Milazzo et al. 1998). Structure refinements on cation-exchanged varieties were performed by Bauer and Baur (1998).

Chemical composition:
	All gismondine has Ca-dominant compositions. Through careful sample selection and analysis of 17 gismondine samples Vezzalini and Oberti (1984) demonstrated that K + Na is generally less than 0.12 atoms per unit cell. Those samples with K greater than 0.08 probably have intergrown with phillipsite. These analyses also show that the water content is slightly variable from 16.5 to 18.5 molecules per unit cell. Artioli et al. (1986) suggest that at least some of the variation is a result of mixed 6- and 7-coordination of Ca. A Ba-dominant composition of gismondine has been found in lead-smelting slags in Yorkshire and Derbyshire (Braithwaite et al. 2001).

Occurrences:
	Gismondine occurs in silica-undersaturated environments, whether in basalt cavities or as late stage hydrothermal alteration phases. Because it is intimately associated with phillipsite, it is likely that the temperature at which crystallization occurs is between 25°C, surface conditions, and about 90°C, for example, phillipsite and gismondine in Iceland geothermal fields (Kristmannsdóttir and Tómasson 1978, p. 284). Some representative occurrences of gismondine in basalt cavities are the following: several localities in Austria mostly in nepheline basalt and associated with gonnardite and phillipsite; in Bohemia, Czech Republic, in basalt and leucite tephrite; various localities in Eifel District, Germany, in vesicles in nepheline basalt and in xenoliths in the basalt and is associated with phillipsite, gonnardite and many others; in vesicles of olivine basalt in eastern Iceland; the type locality is in leucitic basalt at Capo di Bova in Rome area of Italy; in olivine basalt flows of County Antrim, Northern Ireland; and in melilite nephelinite tephra of the scoria cone, Round Top, Honolulu, Hawaii. Other types of occurrences of gismondine include miarolitic cavities in granite Brisbane, Queensland, Australia, where it is associated with prehnite, laumontite, and sulfide minerals; in metapyroxenite with other zeolites, Ontario, Canada; breccia cavities with analcime in nepheline syneite, Mont Saint Hilaire, Quebec, Canada.; and in veins and intensely sheared metaophiolitic rocks (pumpellyite-actinolite facies) and serpentinite in Liguria, Italy (Argenti et al. 1986).

References:
	Argenti, P., Luchetti, G. and Penco, A.M. 1986. Zeolite-bearing assemblages at the contact Voltri Group and Sestri-Voltaggio Zonw (Liguria, Italy). N. Jahrb. Mineral., Mh., 1986, 229-239. Artioli, G., Rinaldi, R., Kvick, Å. and Smith, J.V. 1986. Neutron diffraction structure refinement of the zeolite gismondine at 15 K. Zeolites 6, 361-366. Bauer, R.M. and Baur, W.H. 1998. Structural changes in the natural zeolite gismondine (GIS) induced by cation exchange with Ag, Cs, Ba, Li, Na, K and Rb. Eur. J. Mineral. 10, 133-147. Braithwaite, R.S.W., Dyer, A., Lamb, R.P.H. and Wilson, J.I. 2001. Gismondine-Ba, a zeolite from the weathering of slags. J. Russell Soc. 7, 83-85. 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. Fischer, K. and Schramm, V. 1971. Crystal structure of gismondite, a detailed refinement. In Molecular Sieve Zeolites. Am. Chem. Soc., Adv. Chem. Ser. 101. 250-258. Gismondi, C.G. 1817. Osservazioni sopra alcuni fossili particolari de’ contorni di Roma. Giornale Enciclopedico di Napoli, Anno XI, 2, 3-15. Kristmannsdóttir, H. and Tómasson, J. 1978. Zeolite zones in geothermal areas in Iceland. In, Sand, L.B. and Mumpton, F.A. (eds). Natural Zeolites: Occurrence, Properties, Use, Pergamon Press, Elmsford, New York, 277-284. Leonhard, K.C. von 1817. Die Zeagonit, ein neues Mineral vom Capo do Bove bei Rom. Taschenbuch für die gesammte Mineralogie mit Hinsicht auf die neuesten Entdeckungen 11, 164-168 (from Gismondi 1817 and Coombs et al. 1997). Milazzo, E., Artioli, G., Gualtieri, A>, and Hanson, J.C. 1998. The dehydration process in gismondine: An in situ synchrotron XRPD study. Proc. IV Convegno Nazionale Scienza e Techologica della Zeoliti, Cernobbio (Como) Italy, 160-165. Reeuwijk, L.P. van 1971. The dehydration of gismondine. Am. Mineral. 56, 1655-59. Rinaldi, R. and Vezzalini, G. 1985. Gismondine; the detailed X-ray structure refinement of two natural samples. In Zeolites; Synthesis, Structure, Technology and Application (eds. Drzaj, B., Hocevar, S. and Pejovnik, S.) Elsevier, Amsterdam, The Netherlands, 481-492. Vezzalini, G. and Oberti, R. 1984. The crystal chemistry of gismondines: the non-existence of K-rich gismondines. Bull. Minéral. 107, 805-812.