Gonnardite is a comparatively rare, fibrous

zeolite Zeolites are a group of several microporous, crystalline aluminosilicate minerals commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ･y where is either a meta ...

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 Klaprot ...

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 In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic Lattice (group), lattices result from stretching a cubic crystal system, cubic lattice along two of its orthogonal pairs by two different factors, res ...

-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 (geometry), cube becomes a rectangular Pri ...

-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 optics, optical element with flat, polished surfaces that are designed to refraction, refract light. At least one surface must be angled—elements with two parallel surfaces are ''not'' prisms. The most fami ...

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

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, the crystalline forms of silica (silicon dio ...

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

tetrahedra In geometry, a tetrahedron (: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular Face (geometry), faces, six straight Edge (geometry), edges, and four vertex (geometry), vertices. The tet ...

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 (: polyhedra or polyhedrons; ) is a three-dimensional figure with flat polygonal faces, straight edges and sharp corners or vertices. The term "polyhedron" may refer either to a solid figure or to its boundary su ...

containing

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

calcium Calcium is a chemical element; it has 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 to it ...

barium Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. Th ...

, 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 com ...

. It occurs with thomsonite and

vesicle Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane * Synaptic vesicle ; In human embryology * Vesicle (embryology), bulge-like features ...

s in the

volcanic rock Volcanic rocks (often shortened to volcanics in scientific contexts) are rocks formed from lava erupted from a volcano. Like all rock types, the concept of volcanic rock is artificial, and in nature volcanic rocks grade into hypabyssal and me ...

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 one travels west from Devonport, the larger township in the Circular Head municipality being Smithton. Accordin ...

, Australia, intergrown with

at Don Hill, Tasmania and in drill holes with chabazite and

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

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 Canadian Shield ( ), also called the Laurentian Shield or the Laurentian Plateau, is a geologic shield, a large area of exposed Precambrian igneous and high-grade metamorphic rocks. It forms the North American Craton (or Laurentia), th ...

.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 (; ; or ) is a cultural region in central France. As of 2016 Auvergne is no longer an administrative division of France. It is generally regarded as conterminous with the land area of the historical Province of Auvergne, which was dis ...

, France, and

type material In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...

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 (Lo ...

, England, registration number BM.1930,166.

References

{{Commons Zeolites Tetragonal minerals Minerals in space group 122