The Corundum crossover is a term I’ve heard a lot in the industry ever since the discovery of Songea Sapphires in Southern Tanzania. It refers to the border between Tanzania and Mozambique, essentially where Tanzania crosses over into Mozambique. This area is a Geological anomaly and has for twenty years been producing revolutionary deposits of Corundum.

When the Tunduru deposit was discovered it was once described as the most important discovery in fifty years.  This deposit is in south eastern Tanzania and sits right on the Mozambique border, here the predominant production was a Ceylon-like blue but as described by legendary dealer Joseph Belmont “Tunduru stones have much better crystal”.

It was the discovery of colour change Sapphire from this area that changed everything and caused a Sapphire rush that saw this deposit played out by the mid-1990s. Soon after those same artisanal miners uncovered a corundum rainbow in nearby Songea.

Songea offered Sapphires in almost every shade and at the top of the price scale sat the, now mythical, Songea ruby, these Sapphires had not only vivid colours but again amazing crystal, a water like transparency that no one in the industry expected from Sapphires.

Winza was a discovery further North but offered Sapphire being found alongside Rubies, sometimes in the same crystal! These stones didn’t crystallize large and 90% was cabochon grade, but that 5 to 10% of gemmy material was the finest clarity and diaphaneity I’ve ever witnessed in corundum…akin to the Burmese material.

The Corundum that was springing up in this area caused a rush, surpassed in numbers only by the scenes being witnessed now in Madagascar, however in terms of quality, these Sapphires may never be surpassed.

Every deposit in southern Tanzania offered something unique, Tunduru gave the world colour change, Songea coloured the Sapphire marketplace in and then Winza offered incredible and unrivalled diaphaneity.

Almost as suddenly as this trail of colour was uncovered by the artisanal mining people of Tanzania it was depleted. It was a fleeting moment in history and I count myself lucky to have pieces in my collection, I don’t think many of us in the industry really recognised how significant this deposit was at the time. It is now, in the years since, that many of us use these deposits as a benchmark, a benchmark, in most cases, that is never met.

In the wake of these colossal deposits being committed to folklore many of the miners crossed the border ‘The Corundum Crossover’ into Mozambique to discover Montepuez, possibly the most significant Ruby mine in operation today. Over the last 10 years, artisanal miners, those that stayed, have occasionally exhumed the trail to find the lost pockets that run from Tunduru to Songea and these rare and fine parcels of colour send shockwaves through the market. I’m glad I got my pieces when I did, because the prices for the same material today are unrecognisable, a staggering difference…gemmy material has seen price rises of up to 20x and the extra fine stones can be up to 100x more than they were even 5 or 6 years ago. These aren’t just collector’s stones, if you have coloured Sapphires from Africa, they are legacy stones.

With the uncertainty in Tanzania now, the outlook or possibility, for many, to add these African miracles to their collection may become about as hard to realise as getting a one carat eye clean natural pink topaz.

The fact is many people in the industry are looking to get out of Tanzania, Petra diamonds had a shipment of diamonds seized this year on their way to Antwerp, the Government seems intent on nationalising the Tanzanite mine and investors just don’t feel safe putting their money into ground there. As a result the price for Tanzanian stones has gone through the roof and it has caused many to speculate that whatever remains of the African rainbow may remain buried within the Corundum Crossover.