The first new vein of the rare mineral Blue John to be discovered in 150 years has been found by accident. The mineral, also known as Derbyshire spar, was found in the Peak District by miner Gary Ridley while he was testing a new stone chainsaw.

Blue John, named after its distinctive colour, was the height of fashion in Regency times and graced the tables of Buckingham Palace and Chatsworth House. But it is only found in one place on earth – beneath Treak Cliff Hill near the village of Castleton, Derbyshire. And the last vein found was in the 19th century.

The new find, dubbed Ridley Vein after its discoverer, emerged at the Treak Cliff Cavern tourist attraction. “It was only because we were trying out a new method of mining using a stone chainsaw that we discovered it,” said Mr Ridley. “I decided to try the new saw in an area of the cavern we’ve never dug before ... just off the tourist route. I couldn’t believe my eyes when, within a few minutes, I had uncovered a substantial deposit.”

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Historically there have been 14 distinct veins of Blue John, with the Ridley Vein now entering the record books as variant No 15. Dr Trevor Ford, a retired senior lecturer in geology at Leicester University, an expert on the mineral, said the find was a “major new development”.

In 2013, miners rediscovered a “lost vein” of Blue John after more than 70 years.

Vicky Turner, whose family have owned and managed Treak Cliff Cavern since the 1940s, said the Ridley Vein has “swirling patterns of purple and blue”. It will be used to make decorative bowls and other pieces.