Gifted a ring for 25th birthday...

My dad got it from an estate sale - he said that it's a "very valuable" stone in the middle, but, im just not so sure about that?? I'd love some feedback from someone who knows more!

It's previous owner did not take very good care of it, but, I do know that the ring is made from sterling silver, and the 6 side-gems are amethyst. If it is of any value, I'd like to take it in for a professional cleaning ☺️