Hi Chris, Oh! I knew there was something else that I should have provided. The hole tapers on entrance and is approx. 1cm in depth. So the actual size of the hole itself, is 1cm x 0.7cm and 1.8cm deep. I hope this makes sense.
I have looked at a considerable amount of the Blenko ranges and not currently convince myself that it is yet. The cobbled and base pattern design is not one I have seen on Blenko products. I can now see, why this post was moved, but IMHO, the hole size and weight would definitely suggest to me that this it is a pen holder paperweight and not meant for a candle. The lead most certainly helped me, 'expand my thoughts'.

Whatever it is it does not contain uranium. Colourless glass never contains uranium. The dull greenish glow is caused by manganese, which is/was used as a decoloriser.
Well, at least we can eliminate uranium. Cadmium was my initial thoughts, but could not understand why the glass glowed a yellowish green. You've now answered that and grateful. I have not heard of manganese being used to discolour glass and certainly will look this up.
I will not rule out this being a possible Blenko product though.