RIO DE JANEIRO — Electric, neon, fluorescent.

The Paraíba tourmaline’s otherworldly range of greenish blues to violet hues has fascinated gemstone lovers since it was discovered in Brazil’s northeastern state of Paraíba in the late Eighties. The Brazilian stone has a high copper content, giving it a distinctive blue that some swear can glow in the dark. They are only found in one location in Brazil, making the Paraíba tourmaline extremely rare, and production has always been scarce.

Now, supply of one of the most expensive gemstones in the world, which has fetched as much as $50,000 a carat, will be further reduced as Brazilian authorities investigate an alleged scheme to illegally mine and export Paraíba tourmalines to Asia and the U.S.

Brazil’s federal police in the past two weeks shut down two mines in Paraíba and arrested six people as part of the probe.

“Police apprehended a lot of material, from rough, uncut stones to lapidated tourmalines, so we know there was a lot of production coming from those mines,” said João Raphael Lima, the federal prosecutor leading the case in the state of Paraíba. “The operation has definitely disrupted business.”

Prosecutors brought criminal charges against six Brazilian businessmen, a state congressman and an Afghani gemstone trader, accusing them of illegal mining, racketeering, tax fraud, environmental crime, money laundering and illegal money transfers, according to court documents.

The police issued an international arrest warrant for Zaheer Azizi, the only foreigner in the group, who’s allegedly a partner at one of the accused companies in Brazil, according to court documents.

According to the case, Parazul, Mineracao, Comercio e Exportacao Ltda had a license to conduct scientific research at a tourmaline mine, but not to explore it commercially. But police found evidence that for at least the past five years, Parazul extracted large volumes of rough tourmalines and sent them to Mineração Terra Branca, in neighboring Rio Grande do Norte state. There, the Paraíba tourmalines would receive legitimate certificates describing the gems as regular tourmalines, court documents show. They would then go to Minas Gerais, Brazil’s main gemstone-producing state, to be lapidated and exported.

The scheme allowed companies to export the tourmalines paying much lower taxes, according to federal prosecutor Lima. Once abroad, Azizi would allegedly sell the gems through his companies Azizi Enterprises Co. Ltd and Azizi Gems and Minerals Co. Ltd., both based in Bangkok, court documents revealed. The company’s Facebook page Azizi Gems & Jewellery claims, “We are the sole provider of Paraíba Tourmaline from Brazil.”

Valberto Alves de Azevedo Filho, one of Parazul’s lawyers, said the company never explored the mine commercially, only for research purposes. Azizi didn’t respond to phone messages left at his companies in Bangkok, nor to e-mail messages seeking comment.

The Paraíba tourmaline’s luminescence comes alive even in low light. Set in a white gold ring with diamonds, the center stone of an H. Stern piece is a spectacularly large neon blue Paraíba tourmaline, part of the Brazilian jeweler’s collection at its flagship in Rio de Janeiro. With hotter than ever demand for colored gemstones, H. Stern receives constant requests for pieces with Paraíbas, especially from foreign clients.

“Demand for Paraíba tourmalines is always very strong because the color is so amazing,” Robert Weldon, a gem and jewelry expert at the Gemological Institute of America, told WWD.

The stone was discovered in 1987 by Heitor Dimas Barbosa, a Brazilian miner who claims that an inner voice guided him to a hill in the São José da Batalha district, an arid and impoverished area of Paraíba state. He says he had a hunch that he would find something exceptional.

“The gem people went completely crazy” when the Paraíba tourmaline first appeared at gemstone and jewelry shows, Weldon said. The gems enjoyed unrivaled success until the early Aughts, when copper-bearing tourmalines from Mozambique arrived on the market, stunning buyers with similar electric blue-green colors. Copper-bearing tourmaline deposits had also been found in Nigeria, but colors were paler. Dealers of the African stones, eager to ride on the Brazilian material’s success, labeled their tourmalines by the same name.

“The name has become a brand,” Weldon said, adding, however, that the colors of the African varieties are not as saturated as the original Brazilian stones.