Well I did buy it. It arrived today. And I am 99.99% sure it's Monart. If it's not, I'll eat my lunch
What I thought was mica is in fact masses of gold aventurine/copper aventurine - completely smothered in aventurine and random bubbles which is why it's so incredibly difficult to photograph - it looks amazing under artifical lighting.
Not cased, has an internal layer then a layer of bubbles I think, then a layer of aventurine in amber. The base is a little strange, polished flat but the pontil mark is fine ground twice making a figure of eight. And it's a bit thicker than my other Monart in the same shape.
Still, I'm sure in my bones it's Monart. What do you all think and what colour way would it be?
I'll add a few more pics below of the close ups.