elbaite

tourmaline

lepidolite

montebrasite

Elbaite

Images

Formula: Na(Al1.5Li1.5)Al6(Si6O18)(BO3)3(OH)3(OH)
Cyclosilicate (ring silicate), tourmaline group, elbaite-liddicoatite series, dravite-elbaite series, and the elbaite-schorl series.
Varieties of elbaite:
Achroite - colourless
Indicolite - blue
Paraíba tourmaline - brilliant blue-green
Rubellite - red or pink
Tsilaisite - manganese-bearing elbaite
Verdelite - green
Watermelon tourmaline - green exterior, pink interior

Causes of colour in elbaite

Pure elbaite would be colourless because none of the elements in its formula is a chromophore, but colourless elbaite is virtually unknown in nature. If pink elbaite is heated to 500oC it becomes colourless, but if it is irradiated the colour intensifies. The reason for this is as follows.
The element potassium is common in feldspars, and 0.01% of potassium is a weakly radioactive isotope that emits gamma rays that can penetrate more than 10 cm of rock, hence there is always natural radiation from feldspar-bearing rocks. Elbaite usually contains some Ti, Fe and Mn as impurities. Pink elbaite must be low in Ti and Fe and must have some Mn. Fe alone causes it to turn blue and Fe and Ti together cause the elbaite to turn green. If gamma rays strike an Mn2+ ion they may dislodge an elecron, thus oxidising Mn2+ to Mn3+. Mn2+ is a weak absorber of light, so it does not cause colouration, but Mn3+ is a strong absorber of light and hence colours the elbaite pink. This process occurs over a long expanse of time, and is incomplete in natural samples of pink elbaite, but exposure to stronger radiatiion in the laboratory speeds up the process and produces a much stronger colouration
(https://www.youtube.com/watch?v=ejucgGmeJMA).

Specific gravity: 2.9 to 3.1
Hardness: 7½
Streak: White
Colour: Green, red to pink, blue, orange, yellow, colourless
Solubility: Insoluble in virtually all acids except HF (Dana)
Common impurities: Fe,Mn,Cu,Ti,Ca,F
Environments:

Plutonic igneous environments
Pegmatites
Metamorphic environments
Hydrothermal environments

Elbaite is generally a late-stage mineral in cavities in granite and granite pegmatites characterised by hydrothermal replacement, also in some metamorphic rocks and high-temperature hydrothermal veins; it is detrital in sediments; it occurs rarely in aplite schist or dolomite; it is sometimes replaced by muscovite, lepidolite or cookeite (Dana, Webmin, HOM). Tourmaline growth in cavities requires hot fluids (250 to 600oC), hot gases and abundant boron, sodium, lithium and aluminium (Lapis 3.66). Tourmaline crystallises with schorl first and elbaite last (Lapis 3.71).
Inclusions in elbaite include fluorapatite, pyrite, quartz, albite, native copper, graphite, muscovite and pyrochlore (Lapis 3.65).
Associated minerals include quartz, albite, lepidolite, microcline, garnet, muscovite, beryl, apatite and spodumene (HOM).

Localities

At the Sapo mine, Minas Gerais, Brazil, blue-cap elbaite occurs in pegmatite, mostly as loose crystals, but sometimes on an albite or quartz matrix (Min Rec 40.4.290).

At the Batalha mine, Paraíba, Brazil, elbaite occurs in a granite pegmatite cutting a muscovite-quartzite country rock. The presence of copper and to a lesser extent manganese causes the brilliant blue colour; the high concentration of copper is quite unusual. Some crystals have been partially or completely altered to lepidolite. Associated minerals include quartz, lepidolite, schorl, non-cuprian elbaite and niobium-tantalite oxides. Inclusions of native copper and of tenorite have been found in elbaite here. (Min Rec 33-2.127-137).

At the type locality, Fonte del Prete, Elba Island, Tuscany, Italy, elbaite occurs in pegmatite pockets in aplite veins (AM 91.944-952).

At the Kyrk-Bulak granite pegmatite, Turkestan range, Osh region, Kyrgyzstan, elbaite occurs in beryl (FM 53636).

Elbaite from Tanzania has characteristic inclusions of apatite, graphite and pyrite.

The Pulsifer pegmatite, West Mount Apatite Mining District, Auburn, Androscoggin county, Maine, USA, is a rare-element granitic pegmatite that intrudes upper amphibolite facies metapelites and biotite schists that are locally interbedded with calc-silicate rocks. The pegmatite exhibits five distinct zonations.
The border zone consists of fine to mediumgrained equi-granular quartz and plagioclase, and minor biotite and almandine.
The wall zone consists of slightly graphic K-feldspar, quartz, biotite and almandine.
The first intermediate zone is characterised by coarse-grained graphic feldspar and plumose muscovite-quartz aggregates. Almandine and schorl are found as accessory minerals, and rare beryl has been observed.
The first intermediate zone grades irregularly into a coarse-grained plagioclase plus quartz plus muscovite second intermediate zone.
The pocket zone assemblage, which lies below the second intermediate zone and immediately above the garnet seam, consists primarily of cleavelandite and quartz, although locally blocky K-feldspar and muscovite are also abundant. Gem tourmaline, beryl, fluorapatite, hydroxylherderite, gahnite, almandine, columbite-(Mn) and cookeite are among the minerals that have been found within the pocket zone.
The garnet seam is a 1 to 5 cm thick layer of 2 mm to 3 cm euhedral almandine plus anhedral smoky quartz.
Just below the garnet seam lies a zone of undetermined thickness that is composed primarily of blocky graphic albite.
The quarries have all produced gem-quality tourmaline, including green, pink, lilac, blue and colourless elbaite, which occurs most frequently in pockets (R&M 97.1.8-11).

At the Chickering mine, Cheshire county, New Hampshire, USA, elbaite occurs in a montebrasite-siderite assemblage that is associated with secondary phosphates including wardite (R&M 90-5.415).

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