Old blue gemstone

I have opened a box of old stones that I have collected over the years, I came across a guy years ago who had what I described as gold fever, he would buy gold from anyone as long as it was cheap and had no interest in the stones, unless they was diamond, he had been at it for 20 years, sold me a load of filthy dirty stones that I then cleaned. It was great fun seeing all the shapes and colours of the stones. I am sure a few might be really good, but as usual I ain’t done nothing with them yet.
This is the only one like this, I have no idea what it might be. Hoping someone else does