Class : Silicates
    Subclass : Cyclosilicates
    Crystal system : Hexagonal
    Chemistry : Be₃Al₂Si₆O₁₈
    Rarity : Common

Beryl is a silicate characteristic of granitic rocks, pegmatites and pneumatolytic veins ; some of its varieties such as emerald are known in limestones or micashists. Undergoes erosive processes, beryl is altered to bertrandite or kaolinite and is not found in alluvia. Its name comes from the greek berullos, a term that referred to the blue-green gemstones. It is a mineral known since ancient times. Beryl occurs almost always in elongated, striated or vertically fluted, sometimes short or flattened prismatic crystals, rarely terminated (hexagonal section) and commonly grouped into rosettes or columnar aggregates. The ordinary beryl is stony, colorless, green-yellow to green but its gemmy varieties offer a diverse color range. It is an allochromatic mineral (whose color depends on the impurities it contains) :

- pale blue-green, colored by Fe²⁺ (aquamarine variety)
- yellow, colored by Fe³⁺ (heliodor variety)
- pink, colored by Mn²⁺, Cs or Li (morganite variety)
- colorless (goshenite variety)
- green, colored by Cr³⁺ or V⁴⁺(emerald variety)
- red, colored by Mn3+ (red beryl or bixbite variety)

Some much rarer varieties may contain scandium Sc (dark blue bazzite variety), cesium Cs and alkaline (vorobyevite variety, rosterite and blue color maxix), cesium in the channels that deform the hexagonal lattice structure ( pezzottaite), etc...

It is a mineral of major importance for jewelry, especially emerald, aquamarine, heliodore and morganite which are extremely appreciated and used despite a relative fragility. Beryl is also the main beryllium ore with bertrandite, a light metal whose properties are similar to those of aluminum, which is used mainly in alloy with copper, which increases its hardness and resistance.

In France, large crystals of beryl, sometimes up to one meter long, were formerly extracted from the Chanteloube pegmatites in Haute-Vienne. In addition to the gemmy crystals of La Villeder (Morbihan), the Armorican Massif contains beautiful crystals, sometimes decimetric, in the pegmatites of Saint-Jacut-de-la-Mer (Côtes d'Armor) and the island of Batz (Finistère).

Note also the huge stony but bluish beryl from Biauchaud pegmatites near St-Pierre-le-Bourlhonne in Puy-de-Dôme (main photo), where beryl is associated with schorl in a massive quartz.

Beryls and especially aquamarine and emerald never present twinning but some inclusions can be spectacular. We note especially a series of fluid or gaseous inclusions called "helicoidal" or "spiral" inclusions propagating on the axis of elongation of the crystal (photo right). These characteristic inclusions of beryls are due to rapid growth by "screw dislocation" along the axis of elongation.

Because of the importance of aquamarine in jewelry, it is a gemstone that is widely treated. Indeed in nature, the crystals are generally near colorless. To remedy this "problem", aquamarine is very largely heated to improve the color, this treatment is impossible to detect without advanced laboratory equipment. Generally in the market, gemstones with a bright color without inclusion are usually all treated.

Finally in the same way like emeralds and aquamarines, beryls can be synthesized in laboratory, characteristic chevrons inclusions or seeds can be visible under magnification, but only an expert eye can locate them. Further investigations based on the isotopy of oxygen allow to make the difference.

Right photo : Russian hydrothermal reb beryl crystal