The rare mineral, only found beneath Treak Cliff Hill, near Castleton in the Peak District, is so called because of its distinctive colour.
The new vein has been named the Ridley Vein after Gary Ridley, the miner who found it after attempting a new mining method with a stone chainsaw.
He said he could not "believe his eyes" when he came across the Blue John.
The stone was fashionable during the Regency period in the early 1800s and is displayed at Buckingham Palace and Chatsworth House.
Mr Ridley, who manages Treak Cliff Cavern, said he tried out the new saw near the tourist route.
"Having spotted a small amount of crystallisation near the handrail it was just an easy and convenient place to see how well the saw would cut...
"I couldn't believe my eyes when within a few minutes I had uncovered a substantial deposit of Blue John unlike any other vein I had ever seen before."
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" and will be made into decorative bowls and other pieces.
Each vein has its own colour and banding of blue, purple, yellow and white. Historically, there have been 14 distinct veins of Blue John including Millers Vein, Treak Cliff Blue Vein, 5 Vein, 12 Vein and Old Tor Vein.
The Ridley Vein has now entered the record books as variant number 15.
A vein of Blue John stone has been found in Derbyshire, 150 years after the last discovery.