Identifying a 1905 Black Opal Ring: Origin & Markings

Question
I have an opal ring which I bought at an antiques fair a few years ago. I am trying to research its origin. Could you please help. It was sold as being 1905 in date but the only visible mark is 9ct, no other assay marks what so ever. Its a black opal. I have been led to believe that as it doesn't have any British assay marks it could be Australian as they tend to use 9ct in their marks. Thanks

Answer
Hi Karen , this is not so much about the opal as it is about the gold ring.The markings only indicate the gold as you pointed out .
1905 might not have been a black opal but a dark grey base colour .I am away from my reference material at present but will happily check it out further when I return to Aust in the next few days. In the mean time , if you can attach an image it would help greatly to identify it . best regards Rod Keady