Gonnardite is a comparatively rare, fibrous

zeolite Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ･y where is either a metal ion or H+. These p ...

natrolite Natrolite is a tectosilicate mineral species belonging to the zeolite group. It is a hydrated sodium and aluminium silicate with the formula . The type locality is Hohentwiel, Hegau, Germany. It was named natrolite by Martin Heinrich Klapro ...

subgroup. Older papers claim that a complete solid solution exists between tetranatrolite and gonnardite, but tetranatrolite was discredited as a separate species in 1999.American Mineralogist (1999) 84: 1445-1450 A series, based on the disorder of the silicon-aluminum in the framework, appears to exist between Na-rich gonnardite and natrolite, Na₂(Si₃Al₂)O₁₀·2H₂O.Tschernich, Zeolites of the World (1992) Geoscience Press, pages 215 to 225 Gonnardite was named in 1896 after Ferdinand Pierre Joseph Gonnard (1833–1923), who was Professor of Mining Engineering at the University of Lyon, France.

Crystallography

Orthorhombic-bipyramidal class 2/m 2/m 2/m and

tetragonal In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a squar ...

-scalenoidal class 2m (orthorhombic with a very close to b, or tetragonal with a equal to b).
Unit Cell Parameters: a = b = 13.21 Å, c = 6.622 Å, Z = 2Mineralogical Magazine (1998) 62: 548
Space Group: I2d

Crystal habit

Crystals are

prismatic An optical prism is a transparent optical element with flat, polished surfaces that are designed to refract light. At least one surface must be angled — elements with two parallel surfaces are ''not'' prisms. The most familiar type of optical ...

, bounded by and as well as and , and gonnardite also occurs as radial hemispheres. Commonly found as zoned prisms or aggregates with

thomsonite Thomsonite is the name of a series of tecto-silicate minerals of the zeolite group. Prior to 1997, thomsonite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a ser ...

and paranatrolite.

Structure

Gonnardite is a

tectosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide, ) is usually consid ...

belonging to the natrolite group. The natrolite minerals are composed of chains of AlO₄ and SiO₄

tetrahedra In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the o ...

that link to form frameworks. As with all zeolites, there are channels within the framework, and for the natrolite minerals the channels are occupied by

polyhedra In geometry, a polyhedron (plural polyhedra or polyhedrons; ) is a three-dimensional shape with flat polygonal faces, straight edges and sharp corners or vertices. A convex polyhedron is the convex hull of finitely many points, not all on ...

containing

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...

or barium, together with oxygen and water.American Mineralogist (1972) 77:685 Gonnardite has the same framework structure as natrolite, but a disordered Si, Al distribution on the tetrahedral sites. Some of the water sites in the disordered natrolite structure of gonnardite are empty.

Environment

Gonnardite has been found in silica-poor volcanics and

pegmatites A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic co ...

. It occurs with

and

vesicle Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry) In cell biology, a vesicle is a structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer. Vesicles form nat ...

s in the

volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic ...

of The Nut, near

Stanley, Tasmania Stanley is a town on the north-west coast of Tasmania, Australia. It is the second-last major township on the north-west coast when travelling west, Smithton being the larger township in the Circular Head municipality. According to the , Stanle ...

, Australia, intergrown with

at Don Hill, Tasmania and in drill holes with

chabazite Chabazite ()The New Oxford Dictionary of English (1998) - p. 300 "chabazite /'kabəzʌɪt/ noun "A colourless, pink or yellow zeolite mineral, typically occurring as rhombohedral crystals.". is a tectosilicate mineral of the zeolite group, clos ...

and calcite near Guildford, Tasmania.Australian Journal of Mineralogy (2004) 10-2: 59-72 It is also found in nepheline-syenite in the Grenville Geological Province, which is part of the Canadian Shield.The Mineralogical Record 37-4: 285 The type locality (the place where the mineral was first described) is La Chaux de Bergonne, Gignat, Saint-Germain-Lembron, Puy-de-Dôme,

Auvergne Auvergne (; ; oc, label= Occitan, Auvèrnhe or ) is a former administrative region in central France, comprising the four departments of Allier, Puy-de-Dôme, Cantal and Haute-Loire. Since 1 January 2016, it has been part of the new region Au ...

, France, and

type material In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes t ...

from this locality is held at the

Natural History Museum, London The Natural History Museum in London is a museum that exhibits a vast range of specimens from various segments of natural history. It is one of three major museums on Exhibition Road in South Kensington, the others being the Science Museum an ...

, England, registration number BM.1930,166.

References

{{Commons Zeolites Tetragonal minerals Minerals in space group 122