According to the most accepted account, in 1967 a Masai warrior (attribution varies) came across a piece of translucent rock of vivid blue-violet hue some 40km south-east of Arusha, amid the metamorphic rocks of the Merelani Hills, and took the 10,000 carat rough stone to Manuel d'Souza, a Goan tailor and amateur prospector based in Arusha.

De Souza, hoping that the find might prove to be sapphire, in turn showed the stone to Dr John Saul, an MIT-trained geologist and gem dealer in Nairobi, who had already uncovered ruby and aquamarine deposits in Kenya.

"My father immediately realised that this was something special, but obviously not sapphire," says his son, Eric Saul, co-owner with his brother, Mark, of Swala Gem Traders in Arusha. "The colour was too deep. He had never seen anything like it. So he sent it to a lab in Germany, which ascertained that the stones shared the same chemical composition and orthorhombic crystallography as zoisite".

Zoisite itself is nothing to write home about; a relatively widespread mineral discovered in 1805 by the Austrian Baron von Zois. This stone, however, was different. The only transparent, gem-quality crystal of zoisite in existence, and coloured by the rare presence of vanadium, it exhibited a mesmerisingly rich purplish-blue vitreous lustre. With its only known source being a narrow strip of land, 5km by 2km long near Kilimanjaro, beauty and rarity combined.

John Saul hastened to cut the first ever blue zoisite gems - two large oval stones of 15 carats and 19 carats respectively - and sent them to his father, Hyman Saul, the then vice-president of Saks 5th Avenue, a store conveniently located next to Tiffany's, where Henry Platt, great-grandson of Louis Comfort Tiffany, was quick to recognise the value of the find.

Proclaiming this to be "the most beautiful blue stone discovered in over 2000 years", Platt re-christened the gem by the more euphonious name of "tanzanite", and launched it on the market in October 1968.

But despite the over four decades that have passed since the first find, it is still not clear as to who discovered the gem.

But other stakeholders oppose the singling out of Ngoma for credit and two other prospectors, Ali Juuyawatu and Manuel d'Souza, are frequently mentioned as others who could possibly have discovered the gem. Juuyawatu is an expert in mineral prospecting and a household name in tanzanite mining.

Villagers interviewed at Mererani, mention Juuyawatu as the first person they associate with tanzanite. His children, also miners at Mererani insist that it was their late father who discover the tanzanite but that he was not recognised because he died long before the blue stone became internationally acclaimed.

D'Souza, a Tanzanian of Indian origin, was a prospector in the wilds of Tanzania who later worked with Juuyawatu in the mining business, further confusing the issue of who discovered the stone.

Another explanation given is that d'Souza, a tailor, was led to a deposit of tanzanite by Maasai tribesmen including Juuyawatu.

Sammy Mollel, chairman of the Tanzania Mineral Dealers Association (Tamida), says credit should go to d'Souza. The president and chief executive officer of TanzaniteOne, Ian Harebottle gives the credit to Juuyawatu.

Daniel Saitore Kaaya, now 77, who at the time of the discovery was a village elder in an area encompassing Mererani, says it was Juuyawatu who made the discovery but d'Souza who introduced the stone to Henry Platt of Tiffany and Company, the US company which, named the new gem "Tanzanite."

This is a typically African, scenario: few places or things are considered discover until a foreigner promotes and markets them.

To settle the issue of who takes credit for the discovery, Mzee Kaaya says, "Why not simply say a group of herdsmen came across Tanzanite crystals, collected them up, bartered and traded until an unknown trader who knew about gems and the world market introduced it to the rest of the world on their behalf?"

In any case, it is acknowledged that a Tanzanian discovered the gemstone but d'Souza and Juuyawatu (or even Ngoma) went further than the local herdsmen when they officially staked a claim and began commercial mining.

D'Souza, one of the men whom Mollel says should be considered the "discoverers" of the stone, initially believed he had stumbled upon sapphire, but found that the stone was too soft for that.

Laboratory investigations later showed that the stone was a previously undiscovered variety of zoisite, already known in its green form.

D'Souza registered four claims with the mining office. Hot on his heels came a former Greek army officer named Papanicholau who was already involved in several gem ventures in East Africa. The area, which became known as Mererani Hill, was soon dotted with mines.

D'Souza could not control mining on his claimed stake and by his own estimate, up to 80 per cent of the gems from his mines were stolen before he even set eyes on them.

D'Souza and his partner Juuyawatu were later joined by Papanicholau, but the partnership was short-lived, ending in acrimony and court action.

The Tanzania government took control of the mines in 1971, under the name Tanzanian Gemstone Industries, and they were turned over to the State Mining Corporation (Stamico) in 1976. Alas, stamico's mining methods allegedly reduced production drastically.

By the end of the 1970s, Tiffany's which had named and promoted tanzanite, stopped purchasing it because of erratic supply.

In the late 1980s, the government of Tanzania "lost control" of the Mererani mining area and thousands of artisan miners flocked in, but by 1991 the government regained control and has since been issuing licenses to private domestic mining companies.