This is an Imperial Russian silver hallmarked Cossack buckle.
It dates to the (end of ) the ninetheenth century. The design is typical in two parts, with a small miniature Russian dagger on a chain, that closes the buckle when it is stuck through both parts.
The size is approximately 54 x 63 millimeters.
Excellent condition, no damage.
On the back silver hallmarked with silvermark 84 Zolotniki (which corresponds to .875 pure silver) and makersmark “MC”. With Niello finish. Niello is a black mixture, usually of sulphur, copper, silver, and lead, used as an inlay on engraved or etched metal, especially silver. It is added as a powder or paste, then fired until it melts or at least softens, and flows or is pushed into the engraved lines in the metal. It hardens and blackens when cool, and the niello on the flat surface is polished off to show the filled lines in black, contrasting with the polished metal (usually silver) around it.
A true little gem!