Help ID'ing gemstone in vintage ring

[silken]

First of all, I was given this ring by one of my fathers' customers years ago and have had it sat at the back of a drawer for quite some time as it certainly isn't my taste.

According to the hallmark, the ring is 9 carat gold and was hallmarked in 1970 in Birmingham. The makers mark says 'P&W'. However, I am not 100% sure of the stone. It is an emerald cut smoky brownish grey coloured stone with an olive hue under the camera flash. The finish seems to have dulled over the years and could probably do with being re-polished but the question is, what exactly is it? My gut feeling says smoky topaz as I wouldn't personally like to set a smoky quartz or other quartz type stone in a prong setting like this. What does everyone else think? Any other suggestions?

Apologies for the not so brilliant phone pics, I was too lazy to get out my dslr. Apologies also for the grubby jewellery making hands!