An electric blue, 93.94-carat paraiba tourmaline is expected to fetch upwards of $2.5 million when it headlines Sotheby’s Magnificent Jewels and Noble Jewels sale in Geneva on November 8. Dubbed the "Blue Lagoon," the impressive stone is billed as the largest top-quality paraiba tourmaline to ever come to auction.

The remarkable gem is showcased in a lariat-style diamond necklace designed by Geneva-based Adler Joailliers SA. The round, marquise and pear-shaped diamonds cascade down the necklace and collectively weigh more than 76 carats. CEO Allen Adler described the piece, which was created especially for this auction, as a "mix of simplicity and sophistication."

Paraiba is the most prized tourmaline variety. The vivid teal, turquoise and neon blue stones caused a sensation when they were first discovered by prospector Heitor Dimas Barbosa in Brazil’s tropical, coastal state of Paraiba in 1989.

Worldwide demand sparked a mining frenzy and, within five years, the supply beneath “Paraiba Hill” — an area measuring 400 x 200 x 65 meters — was largely tapped out.

In 2001, new Paraiba-like tourmalines were unearthed far across the Atlantic Ocean in Africa. Curiously, the African gems boasted the same color and chemistry as the South American-sourced originals.

Paraiba tourmalines are distinctly different from other varieties of tourmaline because they owe their intense blue color to trace impurities of copper. Others get their color from the presence of iron, manganese, chromium and vanadium. Gem dealers generally refer to copper-infused tourmaline as “Paraiba,” regardless of the origin.

The Blue Lagoon was sourced in southeastern African country of Mozambique.

"The few inclusions found by microscopic examination and the analyzed properties are consistent with those found in copper-bearing tourmalines from the Alto Ligonha district in Northern Mozambique," noted the SSEF (Swiss Gemmological Institute) in an auction appendix letter.

The report also highlighted the gem's impressive size and weight, attractive blue color and excellent purity.

The Blue Lagoon carries a pre-sale estimate of 1.36 million - 2.27 million Swiss francs ($1.5MM - $2.5MM). You can see Sotheby's promotional video by clicking here

Credits: Images courtesy of Sotheby’s.