Vintage cabochon stone

Hello I was looking at some rings online last night and saw some interesting stones , I was surprised by the prices of some of the antique rings. Made me wonder about all the ones I have but not done anything with, like this 6.10ct stone that I think might be a Ruby ? Would have been a stunning gold ring when it was mounted. The bad thing is I know nothing about it. Age where it is from, I saw a stone like this on the Crown Jewels, and also on some belongings from a Indian maharajah,
I think these cabochon rings was popular many years ago