Gaultite		Na4 (H2O)5| [Zn2Si7O18]
Morphology:
	Equant, euhedral crystals are small, about 0.5 mm, multifaceted with the {110}, {021}, {010}, {151}.
Physical properties:
	Cleavage: {101} and {010} perfect. Hardness:  6. D = 2.52 gm/cm3. Luster: vitreous. Streak: white. Fluorescence: strong bright apple-green under short wave UV light.
Optical properties:
	Color: colorless, pale-mauve. Biaxial (+).  α = 1.520, β = 1.521, γ = 1.524, δ = 0.004, 2Vz  = 61°.  Dispersion: r > v weak to moderate.   X = a, Y = c, Z = b
Crystallography:
	Unit cell data: a  10.211,  b  39.88,  c  10.304 Å. Z = 8,  Space group F2dd (Ercit and Van Velthuizen, 1994).
Name:
	Gaultite was described and named by Ercit and Van Velthuizen (1994) for Robert Allen Gault of the Canadian Museum of Nature, Ottawa, Ontario, for his many contributions to the mineralogy of Mont Saint-Hilaire. The type locality is the Poudrette Quarry, Mont Saint-Hilaire, Quebec, Canada. It is the natural occurrence of the synthetic zeolite VPI-7 (Annen et al. 1991).
Crystal structure:
	Gaultite has a framework structure (VSV) consisting of ordered ZnO4 and SiO4 tetrahedra forming strongly deformed eight- and nine-membered ring channels along [101] (Ercit and Van Velthuizen 1994). The eight-membered ring channel is filled with chains of edge-sharing NaO6 octahedra built by framework oxygen atoms and H2O molecules. The nine-membered ring channels host disordered Na (yellow) and H2O (blue). The framework can be constructed from stacks along b of two-dimensional nets composed of four- and eight-membered rings with periodic insertions of tetrahedra between the sheets. The framework also has characteristic three membered rings formed by two SiO4 and on ZnO4 tetrahedra.
Chemical composition:
	The only analysis for gaultite is in Ercit and Van Velthuizen (1994). The empirical formula is Na4.28Zn1.88Si6.99O18 · 5H2O which, considered with structural data, gives the ideal formula Na4Zn2Si7O18·5H2O (Z = 8).
Occurrences:
	The only known occurrence of gaultite was in a cavity of a large (12 m3) sodalite syenite inclusion within nepheline-sodalite syenite at the Poudrette Quarry, Mont Saint-Hilaire, Rouville County, Quebec, Canada (Ercit and Van Velthuizen 1994). Gaultite is a product of late stage fluid activity, as it crystallized after other late stage zeolites and feldspathoids, including  analcime, cancrinite, chabazite, natrolite, phillipsite, and sodalite. From the synthesis conditions of VPI-7, gaultite may have formed at similar temperatures (about 200°C).
References:
	Annen, M.J., Davis, M.E., Higgins, J.B. and Schlenker, J.L. (1991) VPI-7: the first zincosilicate molecular sieve containing three-membered T-atom rings. J. Chem. Soc., Chem. Commun. 1991, 1175-1176. Ercit, T.S. and Van Velthuizen, J. (1994) Gaultite, a new zeolite-like mineral species from Mont Saint-Hilaire, Quebec, and its crystal structure. Can. Mineral. 32, 855-863. Updated: June 2025.