The fossils at that size are fairly inexpensive,the bezel appears to be partially soldered.Probably made by a student/hobbyist.
It could have been made by a hobbyist with a low grade ruby they found at the ruby,sapphire mines in North Carolina.
The silver on the front has fused silver "dust".... [MEDIA]
Cabochons normally have closed backs,the piece was also cast and not fabricated.
Does the stone have a star if you shine a bright light at the top of the stone or go out in clear sky with the sun overhead.
The metal is possibly Nickel/German silver.
It's hard to tell what mines due to the variations at the mines,examples here..... https://waddellgallery.com/pages/turquoise-materials The AP may...
If the diamonds are brilliant they would be sometime after 1920.
You put it on like any bangle bracelet.
The photo is too out of focus to see the type of diamond cut.
It's not moss agate.
Turquoise can start being green or change from blue to green with exposure to water and chemicals/body oils. A few examples of turquoise from...
The stones look like single cut,they don't have the brilliance that a modern cut has.
Brooch to pendant converter,commercial ones have been around for more than 30 years,gold/silversmith's usual handmade them....
Looks like someone tried to repair a broken cross using 10-20% more than the required amount of solder and they didn't do a very good job.
Looks like the bezel has been pried open and maybe the stone replaced.
You won't know what metal it is until it's tested.
The cones look commercially made in the photo.
There is no hardware for a brooch,the 4 "rods/pins" are what connects the center piece to the frame.
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