See also: Beryl (homonymy)

The beryl , or béril, is a Minéral composed of Silicate of Béryllium and Aluminum, of formula Be₃Al₂Si₆O₁₈. Its name comes from the Greek bêrullos , crystal.

Structure

The structure of beryl is made up of Si₆O₁₈ rings which have a plan of Symétrie perpendicular to the main axis, passing by the Atome S of Silicium. These rings form columns parallel with the main axis and are connected between them by rings of four tetrahedrons centered on the Béryllium. Aluminum occupies finally of the octahedral sites. The topology of beryl is thus that of a Tectosilicate (classification of Zoltai) and only the chemical distinction between tetrahedrons centered on the Silicium and those centered on the Béryllium makes it possible to classify this Minéral among the Cyclosilicate S (classification of Machatski-Bragg).

Chemical classification

In alkaline beryls the Lithium can replace the Aluminum in octahedral position, and aluminum can partly replace the Béryllium in tetrahedral position. The electric balance of the structure is carried out by introduction of ions Sodium or Césium into the channels of the structure.

On the basis of alkali contents the beryls are classified in:

• beryl without alkalis: total alkalis lower than 1%;
• poor of alkalis, potassic or sodico-potassic beryl: the Potassium prevails, its content lying between 0,5 and 1%;
• sodic beryl: the Sodium prevails, its content lying between 0,5 and 1%;
• beryl sodico-litifère: Sodium between 0 and 2%, Lithium lower than 6%;
• beryl cesio-litifère: high content of Sodium and Lithium, Cesium higher than 5%.

It is possible that Eau of zeolithic nature is also in the channels, and also of gases like CO₂, Ar and.

Properties

The beryl is the primary source of Béryllium. The hydrothermal synthesis of beryls starting from a mixture of Silica, Alumina and Carbonate of Béryllium can be carried out between 400°C and 850º under pressures from 400 to 2000 bars.

The beryl is easily recognized by its hexagonal morphology and its prismatic faces. In fact, the morphology of beryl consists of prisms {$10\; \backslash \; bar\; \{1\}\; 0$} and {$11\; \backslash \; bar\; \{2\}\; 0$}, finished by the pinacoidal {0001}, and of very many bipyramides {$10\; \backslash \; bar\; \{1\}\; 1$} and {$11\; \backslash \; bar\; \{2\}\; 2$}. The crystals are lengthened along axis Z.

Varieties

The transparent varieties are used like invaluable stones in Joaillerie and are:

• the Aquamarine, blue and green-blue;
• the emerald, green because of the presence of Chromium;
• the héliodore, gilded or yellow because of the presence of Iron;
• the Morganite, pink with orange, container Lithium and Cesium;
• the Goshénite, colorless;
• the Bixbite, red.

Paragenesis

The beryl, like the Tourmaline, is a Minéral granitic Pegmatite S. Of variable size, sometimes very large, it is formed at the end of the crystallization of the granitic solid masses, when the magma remaining grew rich in Eau and rare elements compared to the magma by departure. The elements minéralisateurs (Fluorine, Boron) support the development of large crystals. In such pegmatites, the beryl can be associated with the topaz, the Tourmaline, the Muscovite and the Lépidolite, with large crystals of Feldspath S and quartz, with the Spodumène and many oxides of Titane, tantalum etc (Rutile, Columbite etc).

The beryl can also appear in some Syénite S nephelinic, syenites and Marbre S. the emerald variety has a metamorphic paragenesis (Schiste with Biotite).

Layers

The ordinary beryl is the principal beryllium ore.

The New England (Australia) has many layers; the North Carolina (the United States) is also an ordinary source of beryl.

In France, the beryl was announced to Villeder (Morbihan), towards Alençon (Orne), in the Loire-Atlantique (Orvault), close to Bagnères-with-Luchon (Haute-Garonne), around Bessines (High-Vienna) and of Autun (Saône-et-Loire).

Deterioration

The beryl deteriorates with difficulty in Kaolinite, in Bertrandite Be₄ (OH) ₂, in Phénacite, the amphiboloïde épidydimite Na (OHBeSi₃O₇), in cyclosilicate Milarite K₂Ca₄Al₂Be₄Si₂₄O₆₀·(H₂O).

Symbolic system

The Noces of beryl symbolize the 23 years of Mariage in the French folklore.

See too

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