The top of the bezel wasn't rolled over at the top of the stone leaving a gap. Points and square corners of bezels can be a pain with...
Opal made by hobbyist,student,artisan.
Look at this site might help.... https://www.langantiques.com/university/aesthetic-period-1885-1901/
Are you thinking a precious metal stamp would help?Since there is no requirement to mark precious metal objects in the USA,would need to identify...
Looks like water buffalo horn.
Are the black pieces magnetic?
Separate names with a comma.