Elbaite

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Elbaite
8212M-elbaite1.jpg
Elbaite from Male, Mogok, Sagaing, Mandalay, Myanmar (size: 61 x 60 x 52 mm, 198 g)
General
Category Silicate mineral
Formula
(repeating unit)
Na(Li1.5Al1.5)Al6Si6O18(BO3)3(OH)4
Strunz classification 09.CK.05
Identification
Color Green, red to pink, blue, orange, yellow, colorless, multicolored
Crystal habit Prismatic; striated
Crystal system Trigonal
Cleavage Poor/indistinct on {1120} and {1011}
Fracture Sub-conchoidal
Mohs scale hardness
Luster Vitreous
Streak White
Diaphaneity Transparent to opaque
Density 2.9–3.2
Optical properties Uniaxial (-)
Refractive index nω = 1.635–1.650, nε = 1.615–1.632
Birefringence δ = 0.020
Other characteristics piezoelectric and pyroelectric
References [1][2]
Major varieties
Achroite colorless
Indicolite blue
Rubellite red to pink
Verdelite green
Elbaite

Elbaite, a sodium, lithium, aluminium boro-silicate, is a mineral species belonging to the six member ring cyclosilicate tourmaline group, with the following general composituion: Na(Li1.5Al1.5)Al6Si6O18(BO3)3(OH)4 [3]

Elbaite forms three series, with dravite, with fluor-liddicoatite, and with schorl. Due to these series, specimens with the ideal end-member formula are not found occurring naturally.

Elbaite – Elba Island – Topotype deposit

As a gemstone, 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 in schist; and with molybdenite and cassiterite in massive hydrothermal replacement deposits.

Elbaite is allochromatic, meaning trace amounts of impurities can tint crystals, and it can be strongly pleochroic. 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:
    • Red or pinkish-red; rubellite variety (from ruby)
    • Light blue to bluish green; Brazilian indicolite variety (from indigo)
    • Green—verdelite or Brazilian emerald variety
    • Colorless—achroite variety (from the Greek "άχρωμος" meaning "colorless")
    • 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.

References[edit]

  1. ^ Elbaite. Mindat
  2. ^ Elbaite. Webmineral
  3. ^ http://rruff.info/ima/