Seeing a true blue indicolite is practically a once-in-a-lifetime experience for most jewelers and probably most dealers.
David Federman, 1992

Sapphire blue tourmaline! Such stones are very rare. The search for such a stone is like the pursuit of the Holy Grail.

Historically, two Brazilian mines, the Manoel Mutuca in Arauai and the Golconda Mine northwest of the city of Govenador Valadares, are the source of the fabled "sapphire blue" indicolite. The best of these stones have an intense blue primary hue and a turquoise secondary hue, and are known as Mutuca Blue. Stones of this quality are extremely rare. Indicolite is found sporadically throughout the entire region of Minas Gerais.

A fine 5.28-carat slightly greenish blue tourmaline from Brazil. Note the absence of multicolor effect and the limpid transparency of the crystal.

Hue
If cut on the C axis of the crystal, tourmaline with a primary blue hue will face-up blue, but not without just a slight hint of a secondary hue of green (ten to twenty percent). Stones cut in this manner will always be dark in tone because the C axis of the tourmaline crystal is itself very dark. In more conventionally cut stones, the primary hue is indeed a rich medium to deep hue reminiscent of sapphire; however, the gem will always show a green secondary hue. Gems with an eighty-five percent blue primary hue with no more than a ten percent green secondary hue should be considered fine.

As with all tourmaline, incandescent lighting will bring out the secondary hue. Stones that appear almost pure blue in sunlight or incandescent lighting will pick up a distinct greenish secondary hue under the light bulb. All other factors being equal, the bluer the stone the better the stone.

Saturation and tone
Indicolite can be found in all tonal ranges. The stone is most attractive as the tone approaches seventy-five to eighty percent, the ideal tone for blue. Gray is the normal saturation modifier found in lighter-toned indicolite. As with most tourmaline, the gray is punched up by incandescent lighting.

Clarity
Tourmaline in the green-blue range of hues is usually visually flawless. However, an exceptional indicolite, given its extreme rarity, may be forgiven a few minor flaws. The presence of any visual inclusions should, however, dramatically lower the price.

Crystal
Indicolite tends to turn grayish, lose transparency, and appear muddy in incandescent lighting. Again, tourmaline is a daystone and puts its best foot forward in natural daylight and daylight-equivalent fluorescent lighting. The collector should always view tourmaline in incandescent lighting before making a purchase. Although the gem is often compared to sapphire, blue tourmaline will almost never exhibit a transparency comparable to sapphire.

As with all transparent gemstones, all other factors being equal, diaphaneity transparency or crystal will separate the fine from the merely good, the beautiful from the merely pretty. Finer examples of blue tourmaline that hold their hue and that do not close up or turn sooty in incandescent lighting are very rare and are the most desirable examples of this gem variety.

The rarity factor
Blue tourmaline is rare in any size, but the gem is available in fairly large sizes. Prices will decrease above twenty carats.