Elbaite, a sodium, lithium, aluminium boro-

silicate In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is al ...

, with the chemical composition Na(Li_1.5Al_1.5)Al₆Si₆O₁₈(BO₃)₃(OH)₄, is a mineral species belonging to the six-member ring cyclosilicate tourmaline group. Elbaite forms three series, with dravite, with fluor-liddicoatite, and with schorl. Due to these series, specimens with the ideal endmember formula are not found occurring naturally. As a

gemstone A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, ...

, elbaite is a desirable member of the tourmaline group because of the variety and depth of its colours and quality of the crystals. Originally discovered on the island of Elba, Italy in 1913, it has since been found in many parts of the world. In 1994, a major locality was discovered in Canada, at O'Grady Lakes in the Yukon. Elbaite forms in igneous and metamorphic rocks and veins in association with lepidolite, microcline, and spodumene in granite pegmatites; with andalusite and

biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more alumino ...

in schist; and with molybdenite and

cassiterite Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem. Cassiterite was the chief tin ore throughout ancient history and remains t ...

in massive hydrothermal replacement deposits. Elbaite is allochromatic, meaning trace amounts of impurities can tint crystals, and it can be strongly

pleochroic Pleochroism (from Greek πλέων, ''pléōn'', "more" and χρῶμα, ''khrôma'', "color") is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light. Backgroun ...

. Every color of the rainbow may be represented by elbaite, some exhibiting multicolor zonation. Microscopic acicular inclusions in some elbaite crystals show the Cat's eye effect in polished cabochons.

Elbaite varieties

* Colorless: achroite variety (from the Greek "άχρωμος" meaning "colorless") * Red or pinkish-red:

Rubellite Rubellite is the red or pink variety of tourmaline and is a member of elbaite. Rubellite is also the rarest gem in its gem family. It is occasionally mistaken for ruby. These gems typically contain inclusions. Notable places where rubellite ca ...

variety (from ruby) * Light blue to bluish green: Brazilian indicolite variety (from indigo) * Green: Brazilian verdelite variety (from

emerald Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium or sometimes vanadium.Hurlbut, Cornelius S. Jr. and Kammerling, Robert C. (1991) ''Gemology'', John Wiley & Sons, New York, p ...

) * Watermelon tourmaline is a zoned variety with a reddish center surrounded by a green outer zone resembling watermelon rind, evident in cross section slices of prisms, often displaying curved sides. File:Tourmaline achroïte 1(Pakistan).jpg, Achroite File:Tourmaline-195614.jpg, Rubellite File:Tourmaline-Quartz-214670.jpg, Indicolite File:Turmalingruppe-Elbait-Verdelith - in Quarz aus Brasilien.JPG, Verdelite File:Elbait Turmalin DSC 5183.jpg, Watermelon tourmaline Elbaite at Peabody

References

{{Gemstone Sodium minerals Lithium minerals Cyclosilicates Trigonal minerals Minerals in space group 160 Gemstones Tourmalines

Elbaite varieties

See also

References