These silver earrings could be sterling, because they are tarnished and they polish up nicely, but there is no hallmark or 925 stamp on them, so I will just say they may also be costume jewelry. There is a black square in the center which may be a piece of onyx or obsidian inlaid in the center, but also it could be black enamel paint. Without a gem tester (mine broke 2 years ago) I cannot determine if it is a stone or not.
These earrings measures 14.13 mm 5.55 mm thick, and weigh 7.09 grams.
